Tag Archives: identification

The Hedgepeth trial, when DNA statistics put the interpretation of evidence to the test

Justice, News,

A likelihood ratio of 170 septillion was presented to the jury in Durham, North Carolina, at the trial of Miguel Salguero-Olivares, who is accused of murdering Faith Hedgepeth in 2012 [1]. Derived from the analysis of a DNA mixture recovered from the victim’s body, this figure provides extremely strong statistical support for the proposition that the defendant is one of the contributors to the mixture. It is not, however, proof of his guilt. The testimony given on 14 and 15 October 2026 illustrates a central difficulty of forensic DNA evidence, namely understanding exactly what the statistics can establish and which questions they cannot answer.

Nine years of investigation before a genetic identification

On 7 September 2012, Faith Hedgepeth, a 19-year-old student at the University of North Carolina at Chapel Hill, was found dead in her apartment. The investigation generated a large number of biological samples, but the initial DNA comparisons failed to identify a suspect. In 2021, investigative genetic genealogy led detectives to Miguel Salguero-Olivares [2]. The method uses genetic matches with relatives to direct enquiries towards an individual who may be the source of a trace. In this case it identified distant relatives of the suspect, who were then interviewed and provided DNA samples [2]. A sample obtained without his knowledge during a traffic stop, two days before his arrest was announced on 16 September 2021, allowed a direct comparison with his profile [2].

Fourteen years after the events, his trial opened in Durham. The trial sessions held in October 2026 gave a prominent place to the DNA results. Erin Ermish, a forensic scientist at the North Carolina State Crime Laboratory, presented the analyses carried out on samples from the victim’s body and on several items recovered from the scene [1]. Her testimony drew particular attention to the use of likelihood ratios to assess the strength of the DNA comparisons.

What 170 septillion actually means

According to WRAL, a US news outlet, the scientist stated on 15 October 2026 that the results obtained from a sample taken from the victim’s body were 170 septillion times more probable if the mixture originated from Faith Hedgepeth (the victim) and Miguel Salguero-Olivares (the defendant) than if it originated from the victim and an unknown, unrelated individual [1]. As one septillion is 1 followed by 24 zeros, the value can be written 1.7 × 10²⁶ [1].

This figure is a likelihood ratio (LR). It compares the probability of observing the scientific findings under two alternative propositions, usually framed with reference to the positions of the prosecution and the defence. The higher the ratio, the more the findings support the first proposition over the second. It does not mean that the defendant’s guilt is 170 septillion times more probable than his innocence, nor does it represent the probability that the DNA came from him. This distinction is fundamental, since the ratio concerns the probability of the findings given the propositions considered, not the probability that those propositions are true [5].

The value also depends on the alternative proposition chosen. The one used here refers to an unknown, unrelated individual and therefore does not cover the possibility that a close relative of the defendant, who shares part of his DNA, is the source of the mixture. The question arises all the more naturally because the identification was made through relatives, and a ratio calculated against the proposition that a brother of the defendant was the contributor would be considerably lower.

To rule out this possibility, investigators do not rely on the statistical calculation alone. They also examine the suspect’s family circle to identify relatives who could plausibly be alternative sources of the DNA, such as a brother or father living in the area at the time of the offence. Where such individuals exist, it must then be established whether they can be eliminated, either by direct comparison of their DNA profiles or by evidence showing that they could not have been at the scene, such as a verified alibi. If no relative comes into consideration, or if all have been excluded, an unknown unrelated individual is indeed the appropriate alternative for the evaluation.

The other analyses presented at trial also illustrate the range of results. A second sample from the body produced a value of 114 septillion, calculated under the same propositions [3]. For the top of a rum bottle that the prosecution regards as the murder weapon, the scientist reported a likelihood ratio of 48.6 tredecillion, roughly 4.86 × 10⁴³ [3]. This figure, far higher than those obtained for the body samples, does not mean that the bottle provides stronger support for the defendant’s involvement, because the propositions compared were not the same. For the body samples, the alternative proposition paired the victim with an unknown individual, whereas for the bottle it assumed two unknown contributors [3]. The calculation therefore also reflects the rarity of the victim’s own profile, even though the presence of her DNA on an item found in her home was hardly surprising. The defence did ask the scientist whether this choice could affect the value obtained [4].

By contrast, the DNA recovered from the main body of the bottle, an area that had not been analysed initially, could not be associated with either the defendant or the victim [4]. The profiles obtained from beneath the fingernails of the victim’s left hand neither associated the defendant with the sample nor excluded him [3]. These results are not necessarily contradictory, since the quantity of DNA recovered and the composition of mixtures can vary from one area of an object to another. Their interpretation nevertheless requires a clear distinction between the samples concerned and the conclusions each one actually supports.

Procès de Hedgepeth

By Monica Casey, WRAL Durham reporter

Identifying a source does not explain a contact

A DNA match, even one accompanied by an extremely high likelihood ratio, does not necessarily show how the DNA came to be on a surface. The evaluation may address the biological origin of a trace, which forensic science refers to as the source level [6]. It may also seek to discriminate between different activities that could explain its presence, such as direct contact or indirect transfer. This second level, the activity level, requires additional information and, where the scientific data allow, a specific evaluation [7]. A likelihood ratio calculated for the source question therefore cannot be carried over as it stands to the activity question [6].

DNA can persist after contact and be transferred indirectly through a person or an object [7]. Its presence alone therefore does not allow the deposit to be dated precisely or the action that produced it to be established. The nature of the biological material does, however, bear on this evaluation. In the Hedgepeth case, the detection of spermatozoa in intimate swabs considerably narrows the range of plausible activities, without establishing when the deposit occurred or its connection with the killing [3]. The reports presented in court thus provide information on the possible contributors to the DNA mixtures, but they should not automatically be read as demonstrating the circumstances of the murder.

This distinction is central to the guidance of the European Network of Forensic Science Institutes (ENFSI), which recommends that scientific findings be evaluated against clearly defined propositions suited to the issues in the case [5].

The risk of transposing the conditional

One of the best-known errors in the interpretation of scientific evidence is the prosecutor’s fallacy, a term coined by Thompson and Schumann in 1987 [8]. Despite its name, it is not confined to the prosecution and can be committed by anyone involved in a trial. It consists in confusing the probability of observing a result if a proposition is true with the probability that the proposition is true given the result. An everyday example shows that the two are far from equivalent. The probability that a judge in France speaks French is close to 1, whereas the probability that a French speaker is a judge is minute. Nobody would make this confusion here, but it becomes much harder to detect when it involves numerical values derived from a DNA analysis. Reading the 170 septillion as a probability of guilt, an interpretation rejected above, would be one example.

Bayesian reasoning places the contribution of the expert evidence in its proper context. The likelihood ratio measures how strongly the findings support one proposition rather than the other, without indicating on its own the probability that either is true. It acts as a multiplier applied to the view that could be taken of these propositions before the DNA analysis, on the basis of the other evidence in the case, such as the whereabouts of the person concerned or the witness statements obtained. That assessment is a matter for the fact-finder, not the expert [9]. The same likelihood ratio can therefore lead to very different conclusions depending on whether the person was identified through a body of corroborating evidence or solely through a hit on a DNA database such as the FNAEG, the French national DNA database. When the ratio reaches values comparable to those in the Hedgepeth trial, this prior assessment carries much less weight on the source question, and the debate shifts to the choice of propositions, the risk of error and the circumstances of the deposit.

The Sally Clark case in England illustrates the consequences of this confusion. Tried for the murder of her two sons, who died when only a few weeks old, she was convicted in November 1999 after the paediatrician Roy Meadow told the jury that the probability of two sudden infant deaths in a family like hers was 1 in 73 million [10]. The figure had been obtained by squaring an estimate of 1 in 8,543, as if the two deaths were independent, although genetic or environmental factors shared within a family make that assumption highly questionable [11]. Above all, it was understood, including by part of the press, as the probability that the deaths were accidental, in other words as the probability that the mother was innocent [12]. Yet the murder of two infants by their mother is also an extremely rare event, and the only relevant question was the relative probability of the two explanations in the light of the findings [11]. The convictions were quashed in January 2003, mainly because of microbiological results that had not been disclosed to the defence [10]. As early as October 2001, the Royal Statistical Society had publicly condemned the misuse of statistics in the case [11].

The growth of probabilistic genotyping makes this vigilance all the more necessary. Software such as STRmix or EuroForMix can interpret complex mixtures and low-template traces by modelling the phenomena that affect profiles, in particular allele drop-out and drop-in [13]. These systems frequently produce likelihood ratios in the billions, and sometimes values of the same order as those presented in Durham. The value obtained nevertheless depends on the propositions compared, the number of contributors assumed, the model parameters and the population data used, so two analyses of the same profile may yield different values without either necessarily being wrong.

Nor does a likelihood ratio of 170 septillion mean that the risk of error is 1 in 170 septillion. The calculation assumes that the profile was correctly generated and attributed to the right sample. The risks of contamination or sample mix-up, even if small, are generally far greater than such values and, where they are not negligible, can limit the probative value of the DNA evidence much more than the rarity of the profile [14].

Expert evidence that must be understood and open to challenge

Erin Ermish’s cross-examination focused on the analytical methods and on the possibility that samples stored for several years had degraded [3]. The defence also questioned the sampling choices and the results obtained from different parts of the rum bottle [4]. These exchanges show how important it is to make scientific conclusions understandable without altering their scope. A striking figure can give an impression of absolute certainty, whereas its interpretation remains limited to a specific question.

ENFSI recommends in particular that expert reports set out the propositions considered and the limitations of the evaluation [5]. The aim is to enable those who receive the report to understand the strength of the findings without confusing this scientific assessment with the judicial decision. This requirement applies directly to experts, who must explain their results in accessible language without losing the necessary nuance. It also applies to legal practitioners and investigators, whose questions can help determine whether a conclusion genuinely addresses the propositions at issue in the case.

In the Hedgepeth trial, understanding the ratio of 170 septillion therefore requires knowing which samples it relates to and which propositions were used to calculate it. The results obtained from the other exhibits must be examined for what each contributes in its own right, without being overshadowed by the most striking figures.

Interpretation and the true value of the evidence

The scientific testimony heard in Durham is a reminder that a DNA analysis does not necessarily answer every question raised by an investigation. It can provide extremely strong support for a proposition about the origin of a trace without establishing the exact circumstances of its deposit. A likelihood ratio replaces neither the examination of the other evidence in the case nor the assessment of propositions about the facts, which is a matter for the court. For judges and lawyers, the reported value only makes sense in the light of the conditions under which it was calculated. Knowing which sample was analysed, which propositions were compared and whether the evaluation addresses the source of the DNA or the activity that led to its deposit makes it possible to determine what the expert evidence actually establishes. The clarity with which the expert sets out these elements, both in the report and in court, is an integral part of the quality of the work [5].

Références

[1] WRAL. 170 septillion times more likely, Expert testifies about DNA in UNC student murder trial. 15 octobre 2026.
[2] ABC11. Court documents reveal how investigators linked suspect in Faith Hedgepeth’s murder. 24 janvier 2022.
[3] 9th Street Journal. Day 14 of the Faith Hedgepeth trial, Scientist testifies on DNA evidence. 15 octobre 2026.
[4] The Daily Tar Heel. Forensic scientist connects defendant’s DNA to crime scene during Faith Hedgepeth murder trial. Octobre 2026.
[5] European Network of Forensic Science Institutes (ENFSI). ENFSI Guideline for Evaluative Reporting in Forensic Science. Version 3.0, 2015.
[6] Gill P., Hicks T., Butler J.M. et al. (2018). DNA commission of the International society for forensic genetics, assessing the value of forensic biological evidence, guidelines highlighting the importance of propositions, Part I, evaluation of DNA profiling comparisons given (sub-) source propositions. Forensic Science International, Genetics, 36, 189-202.
[7] Gill P., Hicks T., Butler J.M. et al. (2020). DNA commission of the International society for forensic genetics, assessing the value of forensic biological evidence, guidelines highlighting the importance of propositions, Part II, evaluation of biological traces considering activity level propositions. Forensic Science International, Genetics, 44, 102186.
[8] Thompson W.C., Schumann E.L. (1987). Interpretation of statistical evidence in criminal trials, the prosecutor’s fallacy and the defense attorney’s fallacy. Law and Human Behavior, 11(3), 167-187.
[9] Aitken C., Roberts P., Jackson G. (2010). Fundamentals of probability and statistical evidence in criminal proceedings, guidance for judges, lawyers, forensic scientists and expert witnesses. Royal Statistical Society, Practitioner Guide No 1.
[10] Court of Appeal (England and Wales). R v Clark [2003] EWCA Crim 1020, 11 avril 2003.
[11] Royal Statistical Society (2001). Royal Statistical Society concerned by issues raised in Sally Clark case. Communiqué de presse, 23 octobre 2001.
[12] Royal Statistical Society (2002). Lettre au Lord Chancellor relative à la présentation des preuves statistiques dans les procès pénaux, janvier 2002.
[13] Gill P., Gusmão L., Haned H. et al. (2012). DNA commission of the International Society of Forensic Genetics, recommendations on the evaluation of STR typing results that may include drop-out and/or drop-in using probabilistic methods. Forensic Science International, Genetics, 6(6), 679-688.
[14] Thompson W.C., Taroni F., Aitken C.G.G. (2003). How the probability of a false positive affects the value of DNA evidence. Journal of Forensic Sciences, 48(1), 47-54.

Canine DNA: a British database to make dog hair talk

Unclassified,

A dog hair on a car seat or a trace of saliva on a pair of trousers still goes unexamined all too often in forensic casework. In late September 2026, researchers at King’s College London and the Royal Veterinary College announced that they are building a DNA database of the British canine population, with the aim of indicating a dog’s likely breed, and ultimately identifying an individual animal, from traces recovered at crime scenes [1][2].

The project: mapping the genetics of British dogs

The project is led by Denise Syndercombe Court, Professor of Forensic Genetics at King’s College London, and Dr Federica Giangaspero, who developed the database as part of her doctoral research (the “DogID” project), with archival sample support from Professor Brian Catchpole at the Royal Veterinary College [1]. The team’s latest findings have been published in Forensic Science International [1].

The database compiles genetic profiles from a wide range of breeds present in the United Kingdom (Labradors, Dachshunds, Cocker Spaniels, Pugs and others) in order to establish a reference population [1]. This is what gives a match its statistical weight: without knowing the frequency of a given profile within the canine population, an expert cannot tell a court what a “match” is actually worth. “Dogs are such a big part of our lives – but often overlooked in forensics. They can leave traces of their DNA at crime scenes,” explains Denise Syndercombe Court [1].

Why canine DNA matters to investigators

Animal hairs transfer readily onto clothing, car seats and carpets. At a scene, however, they are frequently classified as “non-human” and set aside without analysis [3]. Part of the evidence vanishes with them, even though sequencing the mitochondrial DNA of a single hair, as practised at the King’s Forensics laboratory, can be enough to place a suspect at the scene of a kidnapping or an unlawful detention [3]. The team is also working to estimate a dog’s likely breed from samples too small or too degraded for commercial canine ancestry testing [3].

Applications range from suspect-to-scene association to the formal identification of a dog involved in an attack on a person or on livestock, as well as dog theft and trafficking [1][2]. A precedent already exists, in cats: in 2013, hairs recovered from the curtain wrapped around a victim’s body, compared against a feline mitochondrial DNA database built by the University of Leicester, helped secure David Hilder’s manslaughter conviction in Portsmouth [5].

Non-human DNA: a field still underused

If animal DNA remains marginal in forensic laboratories, it is above all for want of reference databases, validated kits and interpretation standards comparable to those established for human DNA. A documented, published population database removes part of that obstacle: it makes it possible to quantify the value of a match and to defend that conclusion under adversarial scrutiny.

France is not starting from scratch. Since 1992, the IRCGN, the French gendarmerie’s forensic science institute, has operated a wildlife forensics department, the Département faune et flore forensiques (DFFF), attached to its human identification division. Its experts already examine traces of animal origin, including hair, feathers, blood and soft tissue, to identify a species by molecular methods and to link places or people through an animal, notably in cases of wildlife trafficking, poaching and animal cruelty [6]. The British project goes a step further in aiming at individual identification and breed prediction, both of which require dedicated population databases.

Whether such databases will be built for local canine populations, in France and elsewhere, and under what conditions these analyses will be accepted in court, remains to be seen.

Sources

[1] King’s College London — Cracking crimes with canines: forensics experts build database of dog DNA, communiqué du 28 septembre 2026
[2] The Guardian — DNA database of UK dogs could help police collar criminals, 25 septembre 2026
[3] King’s College London — Dog bites to kidnapping: how King’s Forensics uses canine DNA to solve crime, avril 2023
[4] Forensic Magazine — Forensics Experts Build Database of Dog DNA to Help Solve Crimes, 28 septembre 2026
[5] NBC News — Cat of the Baskervilles: Pet DNA helps convict British killer, août 2013
[6] Gendarmerie nationale — Département faune et flore forensiques (DFFF), IRCGN

What does DNA on a domestic violence victim really prove?

News,

A bite and a strangulation are two common acts in domestic violence, yet they leave very different genetic traces. That is one of the lessons from research to be presented in late October at ISHI 37, the largest annual international meeting devoted to DNA-based human identification [1]. The findings speak to a real difficulty in intimate partner violence cases. Finding a partner’s DNA on the victim’s body is not enough to establish how it got there, particularly when the two people live together and are in regular contact.

The paradox of DNA between partners

In most criminal cases, detecting a suspect’s DNA profile on a victim carries considerable probative weight. That reasoning largely breaks down in domestic violence cases. Partners live together and share the same bed, the same bathroom, the same clothes and countless everyday contacts. Each partner’s DNA is therefore very often found on the other [2]. Specialists call this background DNA, meaning genetic material that has built up through ordinary cohabitation rather than through any specific act.

The question that matters is then no longer really whose DNA it is. It becomes which activity led to its deposition, an ordinary contact of shared life or an act of aggression. This is what Daniel Arend, a young researcher featured in the Student Ambassador programme of the ISHI 37 symposium, is trying to put on an objective footing [1]. His work examines the transfer, persistence, prevalence and recovery of DNA (DNA-TPPR) in two acts emblematic of domestic violence, biting and strangulation [1].

Bites leave a different kind of trace

Daniel Arend’s research looks in particular at DNA recovery after simulated bites. According to the interview published by the organisers ahead of the meeting, bitten areas yielded near-complete profiles of the biting individual in many samples up to 16 hours after contact, the longest interval studied, even though the volunteers had returned to their usual activities [1]. The person who bit was often the major contributor to the mixture, whereas that person generally appeared only as a minor contributor when no biting had occurred [1]. These results should nonetheless be treated with caution, as they have not yet been published in a peer-reviewed journal.

Such persistence is not surprising in light of earlier work on salivary DNA. A study published in 2011 found that a full male profile could still be obtained 96 hours after saliva had been deposited on unwashed skin, in 8 of 9 experiments [3]. A bite can therefore leave a trace whose interpretation differs markedly from that of a simple skin contact.

The strangulation problem

Simulated strangulation involving skin-to-skin contact alone, by contrast, mostly produced only partial profiles [1]. These profiles were often impossible to distinguish from the background DNA associated with cohabitation [1]. The observation echoes research on manual strangulation going back to the late 1990s. Early work showed that the assailant’s DNA could be typed from epithelial cells transferred to the victim’s neck [4]. About a decade later, a British team found that even without any assault, nearly a quarter of the neck areas swabbed from 24 adult volunteers already carried non-donor alleles [5]. A Norwegian study later observed that among participants living with a partner, the partner’s DNA persisted on the neck and accumulated over the course of the day [2]. A neck swab showing the partner’s DNA may therefore prove nothing about strangulation, while a weak or partial profile is no more able to rule it out.

What this means for investigators and expert witnesses

For investigators and forensic practitioners, these data argue for early, targeted swabbing of bite sites, whose evidential value appears to hold over several hours, and for considerable caution when relying on neck swabs from partners who live under the same roof. For expert witnesses, judges and prosecutors, they support the evaluative approach advocated by the European Network of Forensic Science Institutes (ENFSI). This approach asks the scientist to assess the probability of the findings given competing propositions, framed here at the activity level, while taking into account the time elapsed, the victim’s activities and the context of cohabitation, rather than stopping at the mere presence of a DNA profile [6].

Daniel Arend’s work is part of this shift. Its value lies in the effort to generate data that document these situations more thoroughly, rather than treating the mere presence of a profile as direct proof of the alleged activity [1].

Findings that remain preliminary

The scope of this work still calls for caution. Daniel Arend’s results concern experimental scenarios and will be presented as a poster at ISHI 37 [1]. They do not yet amount to a study published in a peer-reviewed journal. They do, however, belong to a broader body of research built up over the past 15 years or so on how DNA moves between people who share the same living or working space. A recent Italian study of shared workspaces showed, for instance, that the DNA of one participant’s cohabiting spouse could be found on that participant’s personal items, in this case a credit card, even though the spouse had taken no part in any of the handling experiments [7]. This shared genetic background, largely overlooked twenty years ago, is now regularly invoked to challenge DNA evidence in the criminal courts.

In domestic violence cases, finding a partner’s DNA on the victim is therefore a piece of information that has to be read in context. The trace may well be relevant, but its evidential value also depends on how it could have been deposited and on the alternative explanations consistent with the findings.

Références

[1] Luther T. « Student Ambassador Poster Preview, Daniel Arend on DNA Transfer in Domestic Violence Cases ». ISHI News, 17 septembre 2026. https://www.ishinews.com/student-ambassador-poster-preview-daniel-arend-on-dna-transfer-in-domestic-violence-cases/
[2] Fantinato C., Gill P., Fonneløp A.E. « Non-self DNA on the neck, a 24 hours time-course study ». Forensic Science International: Genetics, 2022, 57, 102661. DOI 10.1016/j.fsigen.2022.102661.
[3] Kenna J., Smyth M., McKenna L., Dockery C., McDermott S.D. « The recovery and persistence of salivary DNA on human skin ». Journal of Forensic Sciences, 2011, 56(1), 170-175. DOI 10.1111/j.1556-4029.2010.01520.x.
[4] Wiegand P., Kleiber M. « DNA typing of epithelial cells after strangulation ». International Journal of Legal Medicine, 1997, 110(4), 181-183. DOI 10.1007/s004140050063.
[5] Graham E.A.M., Rutty G.N. « Investigation into “Normal” Background DNA on Adult Necks, Implications for DNA Profiling of Manual Strangulation Victims ». Journal of Forensic Sciences, 2008, 53(5), 1074-1082. DOI 10.1111/j.1556-4029.2008.00800.x.
[6] European Network of Forensic Science Institutes (ENFSI). « ENFSI Guideline for Evaluative Reporting in Forensic Science », approved version 3.0, 8 mars 2015. https://enfsi.eu/wp-content/uploads/2016/09/m1_guideline.pdf
[7] Onofri M., Tommolini F., Severini S., Gambelunghe C., Lancia M., Carlini L., Carnevali E. « Trace DNA Transfer in Co-Working Spaces, The Importance of Background DNA Analysis ». International Journal of Molecular Sciences, 2024, 25(4), 2207. DOI 10.3390/ijms25042207.

The Missy Woods case, the DNA analyst who shook Colorado’s forensic science system

News,

Sentenced on 8 September 2026 to 10 years in prison, Yvonne “Missy” Woods, a renowned DNA analyst at the Colorado Bureau of Investigation (CBI), altered DNA data for 15 years [1]. More than 1,000 criminal cases are now under review [2]. Beyond the news item itself, the case raises questions for every judicial system, our own included, about the integrity of scientific evidence and the safeguards meant to protect it.

An expert above suspicion

For nearly 30 years, from January 1994 to November 2023, Missy Woods was one of the most respected figures in forensic science in the State of Colorado [1]. A forensic DNA analyst at the CBI laboratories in Jefferson County, she was called upon for the State’s most sensitive cases, including numerous homicides, sexual assaults and cold cases [1][7]. Known for the speed with which she processed her casework, she carried authority in the courtroom, where her testimony often persuaded juries [5]. It is precisely this reservoir of trust that gives the case its particular dimension.

In September 2023, a CBI intern reviewing the quantitation data of historical sexual assault cases noticed an anomaly [1][14]. In a sample processed by Woods in 2018, the DNA quantitation value was missing, while the raw data clearly indicated the presence of male DNA [1][14]. On 3 October 2023, the CBI opened an internal affairs investigation and placed the analyst on administrative leave [2][3]. A check that could have remained routine became, within a few months, one of the largest forensic scandals in American judicial history. To guarantee the independence of the investigation, the CBI entrusted the criminal inquiry to an outside agency, the South Dakota Division of Criminal Investigation [1][2].

Fifteen years of manipulation

The findings of the internal investigation, made public in 2024, establish that Woods falsified data between 2008 and 2023 [3]. As of August 2025, the CBI had identified 1,045 impacted cases, more than 400 of them involving sexual violence [2][6].

To understand Missy Woods’ method, a technical step needs to be recalled. Before establishing a genetic profile, the forensic laboratory measures the amount of DNA contained in a sample and, in some cases, the amount of male DNA [9]. It is this quantitation value that determines whether the analysis proceeds or whether the sample is declared unsuitable for testing [9]. Woods intervened at precisely this stage. She manually deleted or reduced the male DNA values in her laboratory notes, then issued analytical reports concluding that no male DNA was present when it had in fact been detected [1][7].

The prosecution documented 52 reports containing false statements, to which must be added a 53rd report that was technically accurate but worded so as to discourage an investigator from acting on the results [1]. In 41 of these cases, no criminal charges were ever filed, and 32 of them involved women and children who had reported sexual assault [1]. Of the 12 cases in which charges were filed, only 3 went to trial [1]. One of them, a murder trial, resulted in a conviction based on testimony by Woods whose false nature forms the basis of the perjury count [1].

Nothing indicates that Woods fabricated identifications or positive comparisons in order to convict innocent people [1][3]. Her attorney insisted on this point, stating that she had never altered a profile or the result of a comparison [6]. The motive appears to have been throughput, by setting aside complex analyses, meeting deadlines and maintaining her reputation for productivity [5][7]. At the hearing, she described work that had become “an obsession,” against a background of professional burnout [5]. According to several Colorado media outlets, a colleague had nevertheless flagged inconsistencies in her work as early as 2014, and her supervisors had simply asked her to correct the data, without demanding an explanation [3][4][14]. She went on processing sexual assault evidence kits for another 9 years. None of these circumstances lessens the consequences, since every deleted or falsified item could have led to the identification of a potential offender.

Ten years in prison and a system to rebuild

Initially charged with 102 felony counts, Woods pleaded guilty on 23 June 2026 to four felonies, cybercrime, perjury, attempt to influence a public servant and forgery [1][7]. On 8 September 2026, Judge Andrew Poland sentenced her to 10 years’ imprisonment for cybercrime, 6 years for perjury, 6 years for attempt to influence a public servant and 3 years for forgery, followed by 3 years of parole [1][2]. A restitution hearing has been set for 12 November 2026 [1].

The judge described the facts as intentional misconduct by a highly trained professional occupying a position of extraordinary trust [1]. District Attorney Alexis King stressed that her conduct had “compromised the confidence that law enforcement, defendants and their attorneys, victims, and the public must be able to place in forensic evidence” [1].

For the State of Colorado, the bill is only beginning. Every case handled by Woods now constitutes potential grounds for appeal, including convictions supported by several corroborating elements [1][8]. In 2025, the Boulder District Attorney’s Office had the conviction of Michael Clark for the 1994 murder of Marty Grisham vacated, after retesting of the sealed evidence [8]. In August 2026, a Weld County judge dismissed charges in a child sexual assault case solely on the grounds of Woods’ initial involvement [5][8]. Retesting campaigns, notification of prosecutors and defense attorneys, cascading litigation, the cost was already estimated at more than 11 million dollars two years ago [1][8]. The CBI has created an oversight committee for its forensic services, on which District Attorney Alexis King sits [1].

What this case teaches us

For investigators, magistrates and court-appointed experts, the Woods case is a textbook example on several counts.

  • Internal fraud is the blind spot of quality systems. The CBI laboratory was accredited and regularly audited [3]. However, ISO 17025 accreditation, to which most forensic laboratories are subject, including French laboratories accredited by COFRAC, verifies protocols and operating procedures, not the honesty of an analyst who knows them thoroughly and therefore knows their weaknesses [10][11]. Missy Woods evaded controls for 15 years precisely because she was experienced [3]. The most effective safeguards remain technical review of every case by a second analyst, random audits of raw data rather than reports alone, full digital traceability of analytical files, and genuine follow-up of internal reports. The 2014 episode shows that a report without follow-up is worth less than no report at all, since it created the illusion that the control had worked [4].
  • The expert’s reputation is itself a risk factor. The more renowned an expert, the less their conclusions are questioned, whether by colleagues, by counsel or by the courts [4]. The adversarial principle is meant to correct this bias. In France, the parties may request a supplementary expert report or a second expert opinion, and nothing prevents them from requesting access to the raw data, electropherograms included [12]. The Woods case is a reminder that these tools are only useful if they are used, and that a DNA report is no less open to challenge than any other item in the case file.
  • Finally, it should be remembered that DNA evidence is not infallible. Beyond the risks of degradation, contamination or DNA transfer, the analysis and interpretation of results remain human. DNA, often described as the “queen of evidence,” is now present in almost every criminal case. Yet between the biological sample collected at a crime scene or from a sealed exhibit and the testimony given at trial, there are analytical choices, thresholds, software, sometimes artificial intelligence, and specialists who are very much human. It is this entire chain that must be questioned and controlled. The scandals involving Annie Dookhan and Sonja Farak, two chemists at Massachusetts drug laboratories whose fraud led to the dismissal of more than 20,000 convictions, had already demonstrated this [13]. The Woods case now brings the lesson home in the field of DNA analysis, with victims whose complaints, sadly, never led anywhere.

Colorado’s justice system will take years to repair the damage and the image of its laboratories. For the forensic community, the case will stand as proof that an expert report is worth only as much as the person who signs it, and above all that no accreditation dispenses with a second check. les dégâts et l’image de ses laboratoires. Pour la communauté forensique, l’affaire restera comme la démonstration qu’une expertise vaut ce que vaut la personne qui la signe et surtout qu’aucune accréditation ne dispense d’une double vérification.

Références

[1] Colorado First Judicial District Attorney’s Office, Former CBI Lab Analyst Missy Woods Sentenced to Ten Years in Prison, communiqué de presse, Golden, 8 septembre 2026. https://firstda.co/news-update/former-cbi-lab-analyst-missy-woods-sentenced-to-ten-years-in-prison/
[2] Colorado Bureau of Investigation, Yvonne « Missy » Woods Investigation, page officielle consolidant la chronologie de l’affaire, mise à jour septembre 2026. https://cbi.colorado.gov/forensics/yvonne-missy-woods-investigation
[3] Colorado Bureau of Investigation, Colorado Bureau of Investigation Releases Internal Affairs Report into Former Forensic Scientist Missy Woods, communiqué, Lakewood, 5 juin 2024. https://cbi.colorado.gov/news-article/colorado-bureau-of-investigation-releases-internal-affairs-report-into-former-forensic
[4] Colorado Sun, Coworkers raised concerns a decade before former Colorado forensic scientist was found manipulating data in 654 cases, 5 juin 2024. https://coloradosun.com/2024/06/05/yvonne-missy-woods-internal-affair-report-cbi/
[5] Denver Gazette / Colorado Politics, Disgraced ex-CBI analyst Missy Woods sentenced to prison in DNA scandal, 8 septembre 2026. https://www.coloradopolitics.com/2026/09/08/disgraced-ex-cbi-analyst-missy-woods-sentenced-to-prison-in-dna-scandal/
[6] Colorado Sun, Former CBI scientist Missy Woods sentenced to prison in DNA scandal, 8 septembre 2026. https://coloradosun.com/2026/09/08/yvonne-missy-woods-cbi-scientist-sentenced/
[7] Colorado Politics, Missy Woods accepts plea deal, avoids trial on 102 felony counts, 23 juin 2026. https://www.coloradopolitics.com/2026/06/23/missy-woods-accepts-plea-deal-avoids-trial-on-102-felony-counts/
[8] Longmont Leader, Yvonne « Missy » Woods Sentenced to 10 Years for Manipulating DNA Evidence at CBI, septembre 2026. https://www.longmontleader.com/colorado-news/yvonne-missy-woods-sentenced-to-10-years-for-manipulating-dna-evidence-at-cbi-12761644
[9] Butler J. M., Advanced Topics in Forensic DNA Typing, Methodology, Elsevier Academic Press, 2012, chapitre 3 (DNA Quantitation).
[10] ISO/IEC 17025:2017, Exigences générales concernant la compétence des laboratoires d’étalonnages et d’essais, Organisation internationale de normalisation, Genève, 2017.
[11] Décision-cadre 2009/905/JAI du Conseil du 30 novembre 2009 relative à l’accréditation des prestataires de services de police scientifique menant des activités de laboratoire, JOUE L 322 du 9 décembre 2009.
[12] Code de procédure pénale, articles 161-1 et 167.
[13] ACLU of Massachusetts, Over 61,000 dismissed Farak- and Dookhan-related drug charges across more than 37,000 cases, rapport du Special Master, 2019. https://www.aclum.org/?p=8547
[14] KOAA News, A legacy of doubt, Former CBI forensic scientist who mishandled DNA sentenced to 10 years in prison, 8 septembre 2026 (extraits de l’affidavit d’accusation). https://www.koaa.com/news/local-news/a-legacy-of-doubt-former-cbi-forensic-scientist-who-mishandled-dna-sentenced-to-10-years-in-prison

Iris identification post-mortem avec utilisation en police scientifique - Forenseek

Post-Mortem Iris Identification

News,

For a long time, the iris was thought to become unusable almost as soon as a person died. Several recent studies show the opposite, and the most comprehensive of them has just been published in the United States.

The iris is the coloured ring that surrounds the pupil. Its relief, made up of crypts, furrows and striations, forms a texture that belongs to one individual alone and becomes fixed in early childhood, never changing afterwards. A high-resolution photograph is enough to capture it, after which an algorithm encodes it into a template unique to that person and compares it against every record already held in a database. In France, iris biometrics remains very little used, yet for years it has supported the identification of living individuals elsewhere in the world. In the United States, the FBI has turned it into a service in its own right, the NGI Iris Service, fed by a national network in which sheriffs enrol the iris of suspects and convicted offenders at the time of booking. One question nonetheless remained open, one that almost no one had seriously examined. What becomes of this identifier once the person has died?

A certainty that science eventually overturned

When death occurs, the pupil becomes fixed, most often wide open, and the cornea is gradually veiled by a whitish film, the milky sheen sometimes seen in the gaze of the dead. As early as 2001, John Daugman, the British engineer behind automated iris recognition, told the BBC that this twofold change made the task considerably harder. The notion took firm hold, to the point of feeding the claim, repeated as though self-evident, that the iris became unusable within minutes.

The past 15 years have patiently dismantled that certainty, one study after another [3]. As early as 2016, it was established that an iris could still be recognised several days after death [3]. How the body is preserved soon proved to be the decisive factor. Left outdoors, the iris degrades quickly, whereas fingerprints and the face withstand decomposition far better, as Bolme and colleagues observed [3]. At the other extreme, Sauerwein and colleagues recovered irises that were perfectly analysable 34 days after death, on bodies left outdoors but exposed to the cold of winter [3]. The first studies genuinely tracked over time, carried out in Warsaw by Mateusz Trokielewicz and colleagues, reached a conclusion that few specialists had anticipated. Under favourable conditions, the iris can be analysed without notable difficulty 5 to 7 hours after death, and identification sometimes remains possible up to 3 weeks afterwards [4].

The most comprehensive study to date

The most accomplished demonstration is very recent. It comes from a large team bringing together the University of Notre Dame and Michigan State University, led by Rasel Ahmed Bhuiyan, and it has been accepted by a leading biometrics journal [1]. The researchers first assembled an image collection without precedent, more than 10,000 iris photographs gathered from 259 deceased subjects, in visible light as well as near-infrared, the wavelength that best reveals the texture of the iris [1]. For some of them, the interval between death and image capture reached 1,674 hours, close to 70 days [1].

The corpus includes a case never before published, that of a person whose eye was photographed both before and after death, which made it possible to compare the iris of the living individual directly with that of the deceased [1]. It also contains atypical configurations, rarely documented until then, such as an eye dislodged from its orbit by an injury [1]. Adding the few collections already available, the team brought together images of 338 deceased subjects, the largest sample ever assembled on the subject, then ran them through 5 recognition systems, from the oldest to the most recent, some based on artificial intelligence and others already on the market [1]. The results confirm and refine what the literature had hinted at. When the body has been kept in good conditions, current systems still recognise the iris several hours, sometimes several days, after death [1]. Here again, everything hinges on preservation, and the gap can be considerable. A body left in a field at the height of summer will see its iris degrade within a few days, until any comparison becomes impossible. The same body placed in a refrigerated mortuary drawer at a medico-legal institute, at around 6 degrees Celsius, keeps a usable iris for several weeks [1].

For an investigator, a magistrate or a forensic pathologist, the consequence is clear. No fixed deadline marks the moment when the iris would cease to be identifiable. There are only more or less favourable conditions, which will have to be reconstructed and documented in each case.

The study does not stop at measuring performance. It also delivers an open-source software tool, named PMExpert, designed to support the examiner and already in use since 2021 within a United States medico-legal institute [1]. Rather than returning a definitive ‘yes’ or ‘no’, it highlights the regions of the iris on which it relies to match two images, ante-mortem and post-mortem, leaving the expert free to verify and weigh the correspondence [1]. The software and the accompanying data are made available to forensic services free of charge, through the public United States criminal justice data archive [1].

Estimating how long a person has been dead

The same images fed a second piece of research, one that must be carefully distinguished from the first [2]. This one no longer seeks to identify an individual from the iris, but to estimate how long that individual has been dead. Conducted by Rasel Ahmed Bhuiyan and Adam Czajka and presented at the WACV 2025 conference, it draws on European collections and on the new dataset, 348 subjects in all [2]. The principle is nothing new. For centuries, the forensic pathologist has estimated the post-mortem interval from the positive signs of death that evolve at a relatively steady pace, such as algor mortis, the onset of livor mortis, or the appearance and then the disappearance of rigor mortis. What is new lies in the sign chosen and in the way it is read.

Here, what the machine observes is the white veil that gradually spreads across the eye after death. The more advanced it is, the longer ago death occurred. The researchers trained a deep learning model to perform this reading from the iris photograph alone [2]. Accuracy depends, once again, on environmental factors. In the scenario closest to real conditions, when the model must rule on bodies and settings it has never encountered, it is off by an average of about 3 days [2]. It can therefore point to a window, but never to a precise hour. Feasibility is established, yet we remain far from a fully reliable tool for dating death [2].

For the courts, a lead to handle with caution

In practical terms, what use is this in an investigation? Faced with an unidentified body, the eye is photographed, the software proposes a list of possible matches from a database, and an expert then confirms or rules out each of them [1]. The iris will replace neither DNA, nor fingerprints, nor forensic odontology, the three primary identifiers used to formally identify a body. It is an addition to them, above all when those methods take time or prove unusable, for want of ante-mortem data, on bodies that are too degraded or fragmented.

Its main advantage is speed. Comparing the iris of an eye against a biometric database takes only a few seconds, an argument that can weigh heavily when many victims must be identified under time pressure, after a mass-casualty event for example. This ability to reliably identify someone after death nonetheless raises a security concern of the first order. If the iris of a deceased person remains identifiable, one can imagine that a deliberately removed eye, or even a stored image, might be used to unlock a phone or to clear a biometric checkpoint based on this method. The authors anticipated this scenario and adapted software designed to flag fake eyes, a form of presentation attack detection, showing that it very quickly learns to recognise a deceased person’s iris and reject it [1].

Conclusion

The real reach of this advance remains to be measured. The window of opportunity exists, but it closes quickly, as the corneal veil thickens and the tissues decompose. The images needed to train and test the software remain scarce and hard to gather, something the researchers themselves acknowledge as a major obstacle [1]. And no framework yet defines what would make such an identification admissible in court. As long as that framework is missing, the iris of a deceased person is to be weighed like any other expert finding, with its conditions to document and its share of debate.

One obvious point deserves to be stressed above all. Identifying someone from the iris presupposes that this iris is already on file, recorded while the person was alive, when applying for a biometric passport in countries that provide for it, or when gaining access to a secure site through iris recognition. Without that reference, even the most powerful analysis leads nowhere. In France, where the iris feeds no identification file, the technique is therefore, for now, a matter of horizon-scanning more than routine practice. It nonetheless deserves close attention, for it illustrates a deeper trend, that of a forensic science learning to make the body speak when DNA and fingerprints fall silent.

References

  • [1] Bhuiyan R. A., Farmanifard P., Sharma R., Kuehlkamp A., Boyd A., Flynn P. J., Bowyer K. W., Ross A., Chute D., Czajka A. (2026). Beyond Mortality, Advancements in Post-Mortem Iris Recognition through Data Collection and Computer-Aided Forensic Examination. IEEE Transactions on Biometrics, Behavior, and Identity Science, early access. arXiv:2603.26976. https://ieeexplore.ieee.org/document/11063436
  • [2] Bhuiyan R. A., Czajka A. (2025). Forensic Iris Image-Based Post-Mortem Interval Estimation. IEEE/CVF Winter Conference on Applications of Computer Vision, WACV 2025. arXiv:2404.10172.
  • [3] Boyd A., Yadav S., Swearingen T., Kuehlkamp A., Trokielewicz M., Benjamin E., Maciejewicz P., Chute D., Ross A., Flynn P., Bowyer K., Czajka A. (2020). Post-Mortem Iris Recognition, A Survey and Assessment of the State of the Art. IEEE Access, vol. 8, p. 136570-136593.
  • [4] Trokielewicz M., Maciejewicz P., Czajka A. (2024). Post-mortem Iris Biometrics, Field, Applications and Methods. Forensic Science International.

Analyse ADN laboratoire police scientifique transfert

When an absent investigator’s DNA turns up on a sealed exhibit

Forensic police, News,

A case that had gone unsolved for eighteen years is reopened. From a plastic bag kept as a sealed exhibit, analysts obtain a full DNA profile. Run against the staff elimination database, it returns a name, that of an investigator. The trouble is that this investigator was eighty kilometres from the laboratory and had never set foot at the scene or in the exhibit storage room. The profile was nonetheless his. DNA had identified a person with near-certainty on an item he had never handled. Reported in early 2026 by Gao et al. in Forensic Science International: Genetics, this case is a reminder of a distinction that is too often overlooked: knowing whose DNA a sample carries and knowing how it got there are two different questions.

Identifying the source is not explaining the activity

The forensic laboratory’s result answered one question perfectly, the origin of the genetic material, but it offered no reliable information about the circumstances of deposition. This distinction has long shaped the reasoning of forensic geneticists. In 1998, Cook, Evett et al. [1], writing in Science & Justice, proposed a hierarchy of propositions setting out three levels of interpretation, running from the source to the offence itself. The sub-source level, specific to DNA, was added later, notably by Evett et al. in 2002 [2]. Establishing whose biological profile a sample matches sits at the very bottom of this ladder. Explaining how that profile came to be there, on a substrate or at a crime scene, belongs to the activity level, which is higher and far harder to establish. For a judge, the distinction is decisive. A laboratory can state with great confidence that the DNA profile obtained from a biological sample matches an individual’s profile, yet cannot say, with the same assurance, what that presence means.

The four levels of interpretation: a textbook case

The classic Cook and Evett example, a sexual assault case, where each level adds a further layer of inference on top of the one below:

  • Sub-source level:
    “The DNA in the sample comes from the suspect” (rather than from an unknown person). This is what the raw DNA comparison measures directly. It speaks only to DNA, nothing more.
  • Source level:
    “The semen comes from the suspect.” This adds identification of the body fluid, provided it has been established that the stain really is semen.
  • Activity level:
    “The suspect had sexual intercourse with the complainant.” This adds the mechanism of deposition where transfer, persistence and contamination come into play.
  • Offence level:
    “The suspect raped the complainant.” This adds the absence of consent which the expert cannot decide, since that is for the court.

At each step up, science can say a little less, and the weight of the evidence diminishes.

How more sensitive methods changed the picture

The problem is not new, but it has changed in scale as DNA analysis has advanced. Today’s kits can recover usable DNA profiles from just a few cells, where once a far larger amount of DNA was needed. In 1997, van Oorschot and Jones [9] showed that mere contact is enough to deposit DNA. Since then, the literature has documented many routes of transfer, both direct and indirect, surveyed in van Oorschot et al.’s 2019 review [10]. The effect cuts both ways. The very sensitivity that makes it possible to reopen old cases also raises the chance of detecting a DNA profile unrelated to the events in question. Studies remain cautious about frequencies, which vary widely with conditions, so much so that some authors regard secondary transfer as an uncommon event. Generalisation must therefore be handled with care, in both directions.

The risk of DNA transfer in evidence handling

The journey of a sealed exhibit, from the crime scene to the laboratory bench, passes through a series of handling steps during which DNA can move. The packaging of the item itself plays a part. Stella et al. [7] showed in 2026 that this transfer can run two ways: DNA deposited on an item may migrate to the inner surface of the packaging, so that the sought-after profile is missing from the analysis; or it may transfer to another area of the item, where it has no business being and clouds interpretation. Goray et al. [6] noted in 2019 that the outer surface of gloves could carry, alongside the target profile, that of the examiners themselves, particularly when opening and resealing the packaging. It is precisely this risk that the examination protocols used by forensic services are designed to head off, requiring decontaminated gloves changed for each new item. Examination tools pose a comparable problem, described as early as 2015 by Szkuta et al. [8]. That an investigator might contaminate an item or surface after the fact is therefore no far-fetched hypothesis; Fonneløp’s team [3,4] has studied the phenomenon right down to evidence bags themselves.

To explain the presence of this profile on an exhibit the investigator had never come near, Gao et al. [5] rule out item-to-item transfer in favour of a likely airborne route: the DNA is thought to have settled on a colleague’s clothing before detaching as that colleague approached the sample pre-treatment area. Without the staff elimination database, this hypothesis would never have come to light.

What this distinction changes for the evaluation of evidence

For legal professionals, the lesson of this case is not that DNA is unreliable, but rather that a solid genetic identification at the source level can coexist with a fragile explanation at the activity level. The whole risk lies in sliding from one to the other, when the strength of the former colours the assessment of the latter. To guard against this slide, some forensic geneticists argue that the expert should reason explicitly at the activity level and set out the scenarios consistent with the observations. This is notably the position of the School of Criminal Justice at the University of Lausanne and of the European guideline on evaluative reporting [11].

Conclusion :

The case of the investigator who was never at the scene illustrates the stakes better than any theoretical reminder could. His DNA profile, entirely genuine, sat on a sealed exhibit he had never touched, in a case whose scene he had never visited. Without a safeguard that brought another explanation to light, this finding could have been read as a genuine investigative lead backed by a “relevant” DNA profile. A genetic result is worth not only what it identifies, but what it reasonably allows one to infer, and that is never settled on a single trace alone. A DNA profile must be weighed within the wider body of evidence, never in isolation.

References :

  • [1] Cook R., Evett I.W., Jackson G., Jones P.J., Lambert J.A. (1998). A hierarchy of propositions: deciding which level to address in casework. Science & Justice, 38(4), 231-239.
  • [2] Evett I.W., Gill P.D., Jackson G., Whitaker J., Champod C. (2002). Interpreting small quantities of DNA: the hierarchy of propositions and the use of Bayesian networks. Journal of Forensic Sciences, 47(3), 520-530.
  • [3] Fonneløp A.E., Egeland T., Gill P. (2015). Secondary and subsequent DNA transfer during criminal investigation. Forensic Science International: Genetics, 17, 155-162.
  • [4] Fonneløp A.E., Johannessen H., Egeland T., Gill P. (2016). Contamination during criminal investigation: Detecting police contamination and secondary DNA transfer from evidence bags. Forensic Science International: Genetics, 23, 121-129.
  • [5] Gao L. et al. (2026). A rare and atypical case of long-distance indirect DNA transfer: Contamination from an investigator never present at the scene. Forensic Science International: Genetics.
  • [6] Goray M., Pirie E., van Oorschot R.A.H. (2019). DNA transfer: DNA acquired by gloves during casework examinations. Forensic Science International: Genetics, 38, 167-174.
  • [7] Stella C.J., Goray M., Meakin G.E., van Oorschot R.A.H. (2026). DNA transfer in packaging: Investigation of mitigation strategies. Journal of Forensic Sciences, 71(1), 197-210.
  • [8] Szkuta B., Harvey M.L., Ballantyne K.N., van Oorschot R.A.H. (2015). DNA transfer by examination tools, a risk for forensic casework? Forensic Science International: Genetics, 16, 246-254.
  • [9] van Oorschot R.A.H., Jones M.K. (1997). DNA fingerprints from fingerprints. Nature, 387, 767.
  • [10] van Oorschot R.A.H., Szkuta B., Meakin G.E., Kokshoorn B., Goray M. (2019). DNA transfer in forensic science: A review. Forensic Science International: Genetics, 38, 140-166.
  • [11] ENFSI, Guideline for Evaluative Reporting in Forensic Science, 2015

Quand un baiser permet de transférer l'ADN d'une tierce personne sur un mégot de cigarette. Forenseek

Cigarette butts: can a simple kiss mislead DNA interpretation?

News, ,

A classic crime scene issue

Cigarette butts represent a major biological substrate in forensic casework. Rich in epithelial cells deposited through saliva, they generally yield exploitable genetic profiles. In practice, the discovery of a DNA mixture on a cigarette filter is often interpreted as evidence that two individuals smoked the same cigarette or handled it in close succession. However, with the increasing sensitivity of modern quantification and STR amplification techniques, laboratories are now capable of detecting minute amounts of DNA, including those resulting from indirect transfers. The question is therefore no longer simply “Whose profile is this?”, but rather “How did this DNA get there?”

An experimental protocol based on two realistic scenarios

The authors of this pilot study tested two distinct configurations.

First scenario: kiss, then cigarette.
A couple exchanged a deep kiss involving saliva transfer. Each partner then smoked a cigarette at different intervals: immediately, and then 5, 15, 30, 60, 90, and 120 minutes after contact. The objective was to assess whether the partner’s DNA, retained in the oral cavity, could be secondarily transferred onto the cigarette filter.

Second scenario: shared cigarette.
Both partners alternately smoked the same cigarette, reproducing a case of direct co-consumption. Samples were analyzed either immediately after collection or after a 30-day storage period in order to evaluate the impact of time on DNA quantity and quality.

Detectable persistence for up to two hours

In the “kiss then cigarette” scenario, alleles attributable to the non-smoking partner were detected on cigarette butts up to 120 minutes after contact. The quantity of transferred DNA gradually decreased over time but remained detectable under several experimental conditions. In other words, the presence of a minor DNA profile on a cigarette butt does not, by itself, demonstrate that two individuals smoked the cigarette. A prior intimate contact could be sufficient to explain the mixture. These findings align with previous research showing that salivary DNA can persist in the oral cavity for several tens of minutes, or longer, depending on individual and physiological factors.

The determining effect of processing delay

The study also demonstrated a significant decrease in total DNA quantity after 30 days of storage, accompanied by an increase in the degradation index. This phenomenon particularly affects the minor component of the mixture, which is more fragile and more prone to partial loss (allelic drop-out, imbalance). In practical terms, a cigarette butt analyzed promptly may reveal a detectable mixture, whereas delayed processing could result in an apparently single-source profile.

Such temporal variability complicates interpretation and underscores the importance of carefully documenting storage conditions and processing timelines.

The contribution and limits of Y-STR markers

In cases where the female partner smoked after the kiss, Y-STR analyses allowed specific monitoring of the transferred male component. Complete Y profiles were obtained up to one hour after contact, with alleles still detectable at two hours under certain conditions. However, progressive degradation and low template quantities again require caution and contextual interpretation.

Interpreting at the activity level is essential

These findings clearly illustrate the now central distinction between:

  • Source level: whose DNA is it?
  • Activity level: by what mechanism was it deposited?

When a mixture is detected on a cigarette butt recovered from a crime scene, several scientifically plausible scenarios may exist: co-consumption, successive handling, secondary transfer following prior intimate contact, or even a combination of these hypotheses. An expert cannot therefore limit their assessment to identifying the DNA contributors. They must also evaluate deposition mechanisms consistent with current scientific knowledge, taking into account secondary transfer dynamics and the impact of time.

Conclusion

This experimental study, conducted under controlled conditions, does not claim to establish a universal rule applicable to all judicial situations. It does, however, clearly demonstrate that secondary oral transfer onto a cigarette butt is possible and may remain detectable for up to two hours after a simple kiss. At a time when the sensitivity of genetic analysis techniques continues to increase, these results reaffirm a fundamental principle of forensic science: detecting DNA is not, in itself, proof of a particular scenario. Interpretation must be rigorous, contextualized, and grounded in activity-level reasoning in order to avoid overinterpretation before the courts..

Source :

GIANFREDA, Denise, CORRADINI, Beatrice, FERRI, Gianmarco, FERRARI, Francesca, BORCIANI, Ilaria, CECCHI, Rossana, SANTUNIONE, Anna Laura. Preliminary study of mixed traces on cigarette butts and non-self DNA transfer, persistence, prevalence and recovery in different forensic scenarios. Legal Medicine, 2026, vol. 81, article 102803. DOI: 10.1016/j.legalmed.2026.102803.

Analysis hair proteomic forensic Forenseek

Identifying an individual without DNA: Hair shaft proteomic analysis

News, Scientific progress, ,

When a hair or body hair is recovered without its root from a crime scene, no conventional genetic analysis can be performed. Lacking nuclear DNA, this biological material has long offered only limited evidentiary value and could neither support the formal identification of an individual nor allow comparison with national DNA databases. Since few years, however, a major shift has occurred: hair proteomics, which exploits the proteins of the hair shaft to reveal individualizing markers. Thanks to advances in mass spectrometry, this approach now provides a new pathway for identification, particularly useful in cold cases or in situations where DNA is absent or unusable.

A biological evidence long underused

Hairs recovered from crime scenes are frequently rootless, preventing any STR (Short Tandem Repeat) analysis. Traditional alternatives (morphological examination or mitochondrial DNA analysis), offer only limited discriminating power [1][9]. In many cases, these items were classified as “weak traces,” with insufficient probative value. Yet a hair is biologically rich. It is composed mainly of keratins and other structural proteins that exhibit remarkable stability and resistance to heat, aging, and environmental degradation [1]. This robustness has led several research teams to explore another avenue: instead of seeking nuclear DNA where it is absent or degraded, why not rely directly on proteins, some of which vary between individuals?

Figure 1: Structure of a hair shaft. Source: cosmeticsdesign.com

From DNA to proteomics

This technological shift relies on high-resolution mass spectrometry (HRMS), combined with bioinformatic analysis of protein polymorphisms. Recent work has confirmed that hundreds of proteins can be identified in a single hair shaft. Among them, certain markers, SAPs (Single Amino acid Polymorphisms), directly reflect individual genetic variation [2]. A major study demonstrated that a single individual presents, on average, more than 600 detectable protein groups and more than 160 polymorphic markers, yielding Random Match Probabilities (RMP) on the order of 10⁻¹⁴ [2]. This protein signature therefore offers strong discriminating power, in some cases comparable to the informational value of mitochondrial DNA, while avoiding several well-known limitations of the latter [10].

Technical obstacles related to protein extraction, made difficult by the highly cross-linked structure of keratin, have also been partially overcome. Protocols combining controlled heat and reducing agents now allow more efficient and reproducible extraction [3]. These advances make the approach more mature and more suitable for forensic practice.

Analyse protéomique du cheveu pour une identification forensique. Article Forenseek.
Figure 2: Hair proteomic analysis workflow. Proteins extracted from the hair shaft are fragmented and then analyzed by mass spectrometry to identify individual peptide variations. Source: [2] Parker, G. et al., Deep Coverage Proteome Analysis of Human Hair Shafts, Journal of Proteome Research, 2022.

Concrete opportunities for investigations

Hair-shaft proteomics significantly enhances the usefulness of hair traces in investigations. In cold cases, hairs preserved for decades can now provide individualizing information, even when nuclear DNA was unusable at the time of the original analysis [5]. In extreme contexts (fire scenes, carbonized remains, or highly degraded traces), proteins often persist where DNA has degraded, making them particularly valuable [5][6].

In recent investigations (sexual assaults, abductions, violent incidents, close-contact events), head or body hairs without roots recovered from clothing, vehicles, or victims can now contribute to establishing associations or excluding individuals. Even when it does not yield a formal identification, the protein signature may narrow the suspect pool, confirm or refute an investigative hypothesis, and support evidential assessments presented to judicial authorities [4]. From a legal standpoint, this method must be understood as a probabilistic approach, similar in principle to mitochondrial DNA analysis but based on more stable markers [7]. When integrated carefully, it may become decisive in investigative orientations, the re-examination of older cases, or situations previously left unresolved due to lack of nuclear DNA or usable fingerprints.

Technical limits and challenges

Despite its potential, hair-shaft proteomics remains a technique still in maturation. The first limitation lies in the protocols themselves: protein extraction remains challenging due to the resistant structure of the hair shaft, and full standardization has not yet been achieved [3]. A second challenge is the creation of sufficiently large population databases to compute robust Random Match Probabilities [4]. Inter-laboratory validation, essential before any use in judicial contexts, requires testing on hairs from individuals of different populations, ages, environments, and storage conditions [4][6].

Legal integration also presents challenges. Judges and attorneys will need clear explanations of this emerging probabilistic evidence. Classical admissibility requirements (reliability, reproducibility, methodological transparency, statistical robustness), apply fully [7]. To date, no international standard formally regulates the procedure, although preliminary work is underway [8].

Towards standardization and operational integration?

The outlook for the coming years is particularly promising. Several centres, notably Murdoch University and ChemCentre near Perth, Australia, are working on protocol standardization and the development of diverse reference databases [5][6]. Advances in mass spectrometry and bioinformatic tools now make possible a partial automation of analyses and more seamless integration into routine forensic laboratory workflows. For investigators, police officers, magistrates and forensic experts, this evolution requires adapting collection and preservation practices. From now on, any rootless hair should be systematically collected and retained. Even very small or very old samples may contain an exploitable protein signature. This shift in perspective could transform the re-evaluation of cold cases, fire-scene examinations, and the most complex investigations.

Conclusion

Hair-shaft proteomics represents one of the most promising advances of the coming years in forensic identification. By restoring value to traces long considered underexploited, it offers a reliable and robust alternative when DNA is absent, degraded or otherwise unusable. Although judicial integration still requires validation, standardization and appropriate communication, early results clearly indicate that this approach could play a decisive role in complex investigations, degraded scenes and unresolved cases.

References :

[1] Adav, S.S., Human Hair Proteomics: An Overview, Science & Justice, 2021.
[2] Parker, G. et al., Deep Coverage Proteome Analysis of Human Hair Shafts, Journal of Proteome Research, 2022.
[3] Liu, Y. et al., Individual-specific proteomic markers from protein amino acid polymorphisms, Proteome Science, 2024.
[4] Smith, R.N. et al., Forensic Proteomics: Potential and Challenges, Proteomics, 2023.
[5] Murdoch University – Western Australia, Hair Protein Identification Project (2024–2025).
[6] ChemCentre (Western Australia Government), World-first Forensic Proteomics Research Program, 2024.
[7] Henry, R. & Stoyan, N., The Admissibility of Proteomic Evidence in Court, SSRN, 2020.
[8] ISO / ASTM – Guidelines on Forensic Biology & Novel Analytical Methods, 2022–2024.
[9] Anslinger, K., Hair Evidence in Forensic Science, Wiley, 2019.
[10] Budowle, B., Mitochondrial DNA in Forensic Identification, Elsevier, 2018.

Cats — reliable witnesses in criminal investigations?

News,

It is well known that our pets love affection and display unwavering loyalty. What has recently been discovered, however, is that they can also hold irrefutable evidence in the context of a criminal investigation.

Researchers from Flinders University in Australia took a close interest in the cats that inhabit many Australian households — not to study their habits or charming quirks, but for a much more forensic reason. These experts in criminalistics, genetics and forensic medecine sought to determine to what extent these animals could act as receptacles for human DNA and potentially transfer it onto other surfaces.

A single contact is enough to cause transfer

To test this hypothesis, the scientists conducted a study on twenty cats from fifteen households, collecting samples from four different areas: the fur on the head, back and right side of the body, and the skin located on the left flank of the animals.

A significant amount of DNA was recovered, mostly from the cats’ fur and, to a lesser extent, from their skin. Unsurprisingly, most of this genetic material belonged to the cats’ owners. More surprisingly, however, DNA from individuals outside the household was also detected in 47% of the samples—particularly from cats that regularly roamed their neighborhood. This demonstrates that feline fur readily captures human DNA, not only through petting but also via brief, incidental contact. Moreover, the study showed that DNA transfer can also occur in the opposite direction—from the cat to another person or to an object—simply by tapping or scratching the animal’s fur with a bare or gloved hand. In both cases, the recovered traces proved sufficient to identify an individual.

The cat: a silent but relevant witness

For forensic investigators, the findings of this study open up new perspectives in the way a crime scene is approached. From now on, an animal present at the scene can be considered as potential evidence if it is suspected to have come into contact with the perpetrator of a crime. Since their fur acts as a true reservoir of DNA, collecting samples from the areas identified by the researchers could make it possible to identify offenders—or, conversely, to rule out certain suspects.

It should be noted that this ability to capture human DNA is not unique to cats. Dogs, which are also common household companions across the world, have proven to be excellent collectors of genetic material as well.

Read full article here.

The sexome: a potential source of evidence in sexual assault cases

News,

Thanks to new sampling and analytical techniques, forensic science now plays an essential role in solving sexual crimes. In cases where the search for semen fails, the sexome—also referred to as the genital microbiome—could take over and become a complementary, or even decisive, investigative tool.

What is the sexome? At a time when the importance of the human microbiota is being recognized in numerous areas of health, researchers are no longer confined to the studying of the bacterial flora colonizing the skin and the intestine. They are also focusing on the microorganisms that inhabit the male and female genital areas—the genital microbiome. Their work primarily addresses health-related questions, such as the prevention of sexually transmitted infections, but its implications extend further.

A unique microbial signature

A study conducted by a team of researchers from Murdoch University in Perth, Australia, on about a dozen heterosexual couples, demonstrated that each individual possesses a distinctive genital microbial flora. This flora, more abundant in women than in men, is transferred from one partner to another during sexual intercourse. According to Brendan Chapman, forensic scientist and co-author of the study, the discovery of these microbial “traces” could offer an effective alternative for identifying perpetrators of sexual offences.

Identification possible even in condom-protected intercourse

According to the scientists behind this discovery, this new technique could play a decisive role when semen DNA analysis proves problematic. The collection of biological material from victims of sexual assault is now highly advanced and, thanks to genetic databases, enables numerous identifications. However, this method faces several challenges, particularly related to time constraints. Beyond 48 hours, the quantity of sperm cells decreases dramatically and may no longer be sufficient for conclusive DNA analysis. Furthermore, in the absence of ejaculation or when a condom has been used, these biological traces are nonexistent.

By contrast, with the help of advanced sequencing techniques, it is possible to detect the sexual microbial signature transferred from one partner to another in samples collected up to five days after sexual contact. Even more remarkably, these transfers can still be detected after washing the genital area, and—though in smaller quantities—even when a condom has been used. In such cases, explains Brendan Chapman, it is mainly components of the female sexual microbiome that are recovered from the male genital area. This approach could help identify more sexual offenders even in the absence of DNA evidence, without requiring additional samples to be taken from already deeply traumatized victims.

The next step for scientists is to refine the technique by determining which factors can influence the sexome—particularly the vaginal microbiome, which fluctuates with the menstrual cycle—since such variations may affect the accuracy of results. This promising line of research opens new perspectives for forensic science.

Read the full study here.