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Linear Sequential Unmasking–Expanded (LSU-E): A general approach for improving decision making as well as minimizing noise and bias

26 March 2025Articles, Forensic police, Justiceinvestigation, police scientifiqueadmin

Copy of the article Linear Sequential Unmasking–Expanded (LSU-E): A general approach for improving decision making as well as minimizing noise and biais, Forensic Science International: Synergy, Volume 3, 2021, 100161, with author agreement (contact : [email protected])

All decision making, and particularly expert decision making, re quires the examination, evaluation, and integration of information. Research has demonstrated that the order in which information is pre sented plays a critical role in decision making processes and outcomes. Different decisions can be reached when the same information is pre sented in a different order [1,2]. Because information must always be considered in some order, optimizing this sequence is important for optimizing decisions. Since adopting one sequence or another is inevitable —some sequence must be used— and since the sequence has important cognitive implications, it follows that considering how to best sequence information is paramount.

In the forensic sciences, existing approaches to optimize the order of information processing (sequential unmasking [3] and Linear Sequential Unmasking [4]) are limited in terms of their narrow applicability to only certain types of decisions, and they focus only on minimizing bias rather than optimizing forensic decision making in general. Here, we introduce Linear Sequential Unmasking–Expanded (LSU-E), an approach that is applicable to all forensic decisions rather than being limited to a particular type of decision, and it also reduces noise and improves forensic decision making in general rather than solely by minimizing bias.

Cognitive background

All decision making is dependent on the human brain and cognitive processes. Of particular importance is the sequence in which information is encountered. For example, it is well documented that people tend to remember the initial information in a sequence better —and be more strongly impacted by it— compared to subsequent information in the sequence (see the primacy effect [5,6]). For example, if asked to memorize a list of words, people are more likely to remember words from the beginning of the list compared to the middle of the list (see also the recency effect [7]).

Critically important, the initial information in a sequence is not only remembered well, but it also influences the processing of subsequent information in a number of ways (see a simple illustration in Fig. 1). The initial information can create powerful first impressions that are difficult to override [8], it generates hypotheses that determine which further information will be heeded or ignored (e.g., selective attention [[9], [10], [11], [12]]), and it can prompt a host of other decisional phenomena, such as confirmation bias, escalation of commitment, decision momentum, tunnel vision, belief perseverance, mind set and anchoring effects [[13], [14], [15], [16], [17], [18], [19]]. These phenomena are not limited to forensic decisions, but also apply to medical experts, police investigators, financial analysts, military intelligence, and indeed anyone who engages in decision making.

Fig. 1. A simple illustration of the order effect: Reading from left to right, the first/leftmost stimulus can affect the interpretation of the middle stimulus, such that it reads as A-B-14; but reading the same stimuli, from right to left, starting with 14 as the first stimulus, often makes people see the stimuli as A-13-14, i.e., the middle stimulus as a ‘13’ (or a ‘B’) depending on what you start with first.

As a testament to the power of the sequencing of information, studies have repeatedly found that presenting the same information in a different sequence elicits different conclusions from decision-makers. Such effects have been shown in a whole range of domains, from food tasting [20] and jury decision-making [21,22], to countering conspiracy arguments (such as anti-vaccine conspiracy theories [23]), all demonstrating that the ordering of information is critical. Furthermore, such order effects have been specifically shown in forensic science; for example, Klales and Lesciotto [24] as well as Davidson, Rando, and Nakhaeizadeh [25] demonstrated that the order in which skeletal material is analyzed (e.g., skull versus hip) can bias sex estimates.

Bias background

Decisions are vulnerable to bias — systematic deviations in judgment [26]. This type of bias should not be confused with intentional discriminatory bias. Bias, as it is used here, refers to cognitive biases that impact all of us, typically without intention or even conscious awareness [26,27].

Although many experts incorrectly believe that they are immune from cognitive bias [28], in some ways experts are even more susceptible to bias than non-experts [[27], [29], [30]]. Indeed, the impact of cognitive bias on decision making has been documented in many domains of expertise, from criminal investigators and judges, to insurance underwriters, psychological assessments, safety inspectors and medical doctors [26,[31], [32], [33], [34], [35], [36]], as well as specifically in forensic science [30].

No forensic domain, or any domain for that matter, is immune from bias.

Bias in forensic science

The existence and influence of cognitive bias in the forensic sciences is now widely recognized (‘the forensic confirmation bias’ [27,37,38]). In the United States, for example, the National Academy of Sciences [39], the President’s Council of Advisors on Science and Technology [40], and the National Commission on Forensic Science [41] have all recognized cognitive bias as a real and important issue in forensic de cision making. Similar findings have been reached in other countries all around the world—for example, in the United Kingdom, the Forensic Science Regulator has issued guidance about avoiding bias in forensic work [42], and in Australia as well [43].

Furthermore, the effects of bias have been observed and replicated across many forensic disciplines (e.g., fingerprinting, forensic pathol ogy, DNA, firearms, digital forensic, handwriting, forensic psychology, forensic anthropology, and CSI, among others; see Ref. [44] for a review)—including among practicing forensic science experts specif ically [30,45–47]. Simply put, no forensic domain, or any domain for that matter, is immune from bias.

Minimizing bias in forensic science

Although the need to combat bias in forensic science is now widely recognized, actually combating bias in practice is a different matter. Within the pragmatics, realities and constraints of crime scenes and forensic laboratories, minimizing bias is not always a straightforward issue [48]. Given that mere awareness and willpower are insufficient to combat bias [27], we must develop effective —but also practical— countermeasures.

Linear Sequential Unmasking (LSU [4]) minimizes bias by regulating the flow and order of information such that forensic decisions are based on the evidence and task-relevant information. To accomplish this, LSU requires that forensic comparative decisions must begin with the ex amination and documentation of the actual evidence from the crime scene (the questioned or unknown material) on its own before being exposed to the ‘target’/suspect (known) reference material. The goal is to minimize the potential biasing effect of the reference/’target’ on the evidence from the crime scene (see Level 2 in Fig. 2). LSU thus ensures that the evidence from the crime scene -not the ‘target’/suspect- drives the forensic decision.

This is especially important since the nature of the evidence from the crime scene makes it more susceptible to bias, because –in contrast to the reference materials- it often has low quality and quantity of information, which makes it more ambiguous and malleable. By examining the crime scene evidence first, LSU minimizes the risk of circular reasoning in the comparative decision making process by pre venting one from working backward from the ‘target’/suspect to the evidence.

Fig. 2. Sources of cognitive bias in sampling, observations, testing strategies, analysis, and/or conclusions, that impact even experts. These sources of bias are organized in a taxonomy of three categories: case-specific sources (Category A), individual-specific sources (Category B), and sources that relate to human nature (Category C).

LSU limitations

By its very nature, LSU is limited to comparative decisions where evidence from the crime scene (such as fingerprints or handwriting) is compared to a ‘target’/suspect. This approach was first developed to minimize bias specifically in forensic DNA interpretation (sequential unmasking [3]). Dror et al. [4] then expanded this approach to other comparative forensic domains (fingerprints, firearms, handwriting, etc.) and introduced a balanced approach for allowing revisions of the initial judgments, but within restrictions.

LSU is therefore limited in two ways: First, it applies only to the limited set of comparative decisions (such as comparing DNA profiles or fingerprints). Second, its function is limited to minimizing bias, not reducing noise or improving decision making more broadly.

In this article, we introduce Linear Sequential Unmasking—Expanded (LSU-E). LSU-E provides an approach that can be applied to all forensic decisions, not only comparative decisions. Furthermore, LSU-E goes beyond bias, it reduces noise and improves decisions more generally by cognitively optimizing the sequence of information in a way that maximizes information utility and thereby produces better and more reliable decisions

Linear Sequential Unmasking—Expanded (LSU-E)

Beyond comparative forensic domains

LSU in its current form is only applicable to forensic domains that compare evidence against specific reference materials (such as a suspect’s known DNA profile or fingerprints—see Level 2 in Fig. 2). As noted above, the problem is that these reference materials can bias the perception and interpretation of the evidence, such that interpretations of the same data/evidence vary depending on the presence and nature of the reference material —and LSU aims to minimize this problem by requiring linear rather than circular reasoning.

However, many forensic judgments are not based on comparing two stimuli. For instance, digital forensics, forensic pathology, and CSI all require decisions that are not based on comparing evidence against a known suspect. Although such domains may not entail a comparison to a ‘target’ stimulus or suspect, they nevertheless entail biasing information and context that can create problematic expectations and top-down cognitive processes —and the expanded LSU-E provides a way to minimize those as well.

Take, for instance, CSI. Crime scene investigators customarily receive information about the scene even before they arrive to the crime scene itself, such as the presumed manner of death (homicide, suicide, or accident) or other investigative theories (such as an eyewitness account that the burglar entered through the back window, etc.). When the CSI receives such details before actually seeing the crime scene for themselves, they become prone to develop a priori expectations and hypotheses, which can bias their subsequent perception and interpretation of the actual crime scene, and impact if and what evidence they collect. The same applies to other non-comparative forensic domains, such as forensic pathology, fire investigators and digital forensics. For example, telling a fire investigator —before they arrive and examine the fire scene itself— that the property was on the market for two years but did not sell, or/and that the owner had recently insured the property, can bias their work and conclusions.

Combating bias in these domains is especially challenging since these experts need at least some contextual information in order to do their work (unlike, for example, firearms, fingerprint, and DNA experts, who require minimal contextual information to perform comparisons of physical evidence).

The aim of LSU-E is not to deprive experts of the information they need, but rather to minimize bias by providing that information in the optimal sequence. The principle is simple: Always begin with the actual data/evidence —and only that data/evidence— before considering any other contextual information, be it explicit or implicit, reference materials, or any other contextual or meta-information.

In CSI, for example, no contextual information should be provided until after the CSI has initially seen the crime scene for themselves and formed (and documented) their initial impressions, derived solely from the crime scene and nothing else. This allows them to form an initial impression driven only by the actual data/evidence. Then, they can receive relevant contextual information before commencing evidence collection. The goal is clear: As much as practically possible, experts should —at least initially— form their opinion based on the raw data itself before being given any further information that could influence their opinion.

Of course, LSU-E is not limited to forensic work and can be readily applied to many domains of expert decision making. For example, in healthcare, a medical doctor should examine a patient before making a diagnosis (or even generating a hypothesis) based on contextual information. The use of SBAR (Situation, Background, Assessment and Recommendation [49,50]) should not be provided until after they have seen the actual patient. Similarly, workplace safety inspectors should not be made aware of a company’s past violations until after they have evaluated the worksite for themselves without such knowledge [32].

Beyond minimizing bias

Beyond the issue of bias, expert decisions are stronger when they are less noisy and based on the ‘right’ information —the most appropriate, reliable, relevant and diagnostic information. LSU-E provides criteria (described below) for identifying and prioritizing this information. Rather than exposing experts to information in a random or incidental order, LSU-E aims to optimize the sequence of information so as to utilize (or counteract) cognitive and psychological influences (such as, primacy effects, selective attention and confirmation bias; see Section 1.1) and thus empower experts to make better decisions. It is also critical that as the expert progresses through the informational sequence, they document what information they see and any changes in their opinion. This is to ensure that it is transparent what information was used in their decision making and how [51,52].

Criteria for sequencing information in LSU-E

Optimizing the order of information not only minimizes bias but also reduces noise and improves the quality of decision making more generally. The question is: How should one determine what information experts should receive and how best to sequence it? LSU-E provides three criteria for determining the optimal sequence of exposure to task-relevant information: biasing power, objectivity, and relevance —which are elaborated below

1. Biasing power.

The biasing power of relevant information varies drastically. Some information may be strongly biasing, whereas other information is not biasing at all. For example, the technique used to lift and develop a fingerprint is minimally biasing (if at all), but the medication found next to a body may bias the manner-of- death decision. It is therefore suggested that the non- (or less) biasing relevant information be put before the more strongly biasing relevant information in the order of exposure.

2. Objectivity.

Task-relevant information also varies in its objectivity. For example, an eyewitness account of an event is typically less objective than a video recording of the same event —but video re cordings can also vary in their objectivity, depending on their completeness, perspective, quality, etc. It is therefore suggested that the more objective information be put before the less objective in formation in the order of exposure.

3. Relevance.

Some relevant information stands at the very core of the work and necessarily underpins the decision, whereas other relevant information is not as central or essential. For example, in deter mining manner-of-death, the medicine found next to a body would typically be more relevant (for instance, to determine which toxi cological tests to run) than the decedent’s history of depression. It is therefore suggested that the more relevant information is put before the more peripheral information in the order of exposure, and –of course- any information that is totally irrelevant to the decision should be omitted altogether (such as the past criminal history of a suspect).

The above criteria are ‘guiding principles’ because:

A. The suggested criteria above are actually a continuum rather than a simple dichotomy [45,48,53]. One may even consider variability within the same category of information; for example, a higher quality video recording may be considered before a lower quality recording, or a statement from a sober eyewitness may be considered before a statement from an intoxicated witness.

B. The three criteria are not independent; they interact with one another. For example, objectivity and relevance may interact to determine the power of the information (e.g., even highly objective information should be less powerful if its relevance is low, or conversely, highly relevant information should be less powerful if its objectivity is low). Hence, the three criteria are not to be judged in isolation from each other.

C. The order of information needs to be weighed against the potential benefit it can provide [52]. For example, at the trial of police officer Derek Chauvin in relation to the death of George Floyd, the forensic pathologist Andrew Baker testified that he “intentionally chose not” to watch video of Floyd’s death before conducting the autopsy because he “did not want to bias [his] exam by going in with pre conceived notions that might lead [him] down one path or another” [54]. Hence, his decision was to examine the raw data first (an au topsy of the body) before exposure to other information (the video). Such a decision should also consider the potential benefit of watch ing the video before conducting the autopsy, in terms of whether the video might guide the autopsy more than bias it. In other words, LSU-E requires one to consider the potential benefit relative to the potential biasing effect [52].

With this approach, we urge experts to carefully consider how each piece of information satisfies each of these three criteria and whether and when it should, or should not, be included in the sequence —and whenever possible, to document their justification for including (or excluding) any given piece of information. Of course, this raises prac tical questions about how to best implement LSU-E, such as using case managers —and effective implementation strategies may well vary be tween disciplines and/or laboratories— but first we need to acknowl edge these issues and the need to develop approaches to deal with them.

Conclusion

In this paper, we draw upon classic cognitive and psychological research on factors that influence and underpin expert decision making to propose a broad and versatile approach to strengthening expert decision making. Experts from all domains should first form an initial impression based solely on the raw data/evidence, devoid of any reference material or context, even if relevant. Only thereafter can they consider what other information they should receive and in what order based on its objectivity, relevance, and biasing power. It is furthermore essential to transparently document the impact and role of the various pieces of information on the decision making process. As a result of using LSU-E, decisions will not only be more transparent and less noisy, but it will also make sure that the contributions of different pieces of information are justified by, and proportional to, their strength.

Références

[1] S.E. Asche, Forming impressions of personality, J. Abnorm. Soc. Psychol., 41 (1964), pp. 258-290
[2] C.I. Hovland (Ed.), The Order of Presentation in Persuasion, Yale University Press (1957)
[3] D. Krane, S. Ford, J. Gilder, K. Inman, A. Jamieson, R. Koppl, et al. Sequential unmasking: a means of minimizing observer effects in forensic DNA interpretation, J. Forensic Sci., 53 (2008), pp. 1006-1107
[4] I.E. Dror, W.C. Thompson, C.A. Meissner, I. Kornfield, D. Krane, M. Saks, et al. Context management toolbox: a Linear Sequential Unmasking (LSU) approach for minimizing cognitive bias in forensic decision making, J. Forensic Sci., 60 (4) (2015), pp. 1111-1112
[5] F.H. Lund. The psychology of belief: IV. The law of primacy in persuasion, J. Abnorm. Soc. Psychol., 20 (1925), pp. 183-191
[6] B.B. Murdock Jr. The serial position effect of free recall, J. Exp. Psychol., 64 (5) (1962), p. 482
[7] J. Deese, R.A. Kaufman. Serial effects in recall of unorganized and sequentially organized verbal material, J. Exp. Psychol., 54 (3) (1957), p. 180
[8] J.M. Darley, P.H. Gross. A hypothesis-confirming bias in labeling effects,J. Pers. Soc. Psychol., 44 (1) (1983), pp. 20-33
[9] A. Treisman. Contextual cues in selective listening, Q. J. Exp. Psychol., 12 (1960), pp. 242-248
[10] J. Bargh, E. Morsella. The unconscious mind, Perspect. Psychol. Sci., 3 (1) (2008), pp. 73-79
[11] D.A. Broadbent. Perception and Communication, Pergamon Press, London, England (1958)
[12] J.A. Deutsch, D. Deutsch. Attention: some theoretical considerations, Psychol. Rev., 70 (1963), pp. 80-90
[13] A. Tversky, D. Kahneman. Judgment under uncertainty: heuristics and biases, Science, 185 (4157) (1974), pp. 1124-1131
[14] R.S. Nickerson. Confirmation bias: a ubiquitous phenomenon in many guises, Rev. Gen. Psychol., 2 (1998), pp. 175-220
[15] C. Barry, K. Halfmann. The effect of mindset on decision-making, J. Integrated Soc. Sci., 6 (2016), pp. 49-74
[16] P.C. Wason. On the failure to eliminate hypotheses in a conceptual task, Q. J. Exp. Psychol., 12 (3) (1960), pp. 129-140
[17] B.M. Staw. The escalation of commitment: an update and appraisal, Z. Shapira (Ed.), Organizational Decision Making, Cambridge University Press (1997), pp. 191-215
[18] M. Sherif, D. Taub, C.I. Hovland. Assimilation and contrast effects of anchoring stimuli on judgments, J. Exp. Psychol., 55 (2) (1958), pp. 150-155
[19] C.A. Anderson, M.R. Lepper, L. Ross. Perseverance of social theories: the role of explanation in the persistence of discredited information, J. Pers. Soc. Psychol., 39 (6) (1980), pp. 1037-1049
[20] M.L. Dean. Presentation order effects in product taste tests, J. Psychol., 105 (1) (1980), pp. 107-110
[21] K.A. Carlson, J.E. Russo. Biased interpretation of evidence by mock jurors, J. Exp. Psychol. Appl., 7 (2) (2001), p. 91
[22] R.G. Lawson. Order of presentation as a factor in jury persuasion. Ky, LJ, 56 (1967), p. 523
[23] D. Jolley, K.M. Douglas. Prevention is better than cure: addressing anti-vaccine conspiracy theories, J. Appl. Soc. Psychol., 47 (2017), pp. 459-469
[24] A.R. Klales, K.M. Lesciotto. The “science of science”: examining bias in forensic anthropology, Proceedings of the 68th Annual Scientific Meeting of the American Academy of Forensic Sciences (2016)
[25] M. Davidson, C. Rando, S. Nakhaeizadeh. Cognitive bias and the order of examination on skeletal remains, Proceedings of the 71st Annual Meeting of the American Academy of Forensic Sciences (2019)
[26] D. Kahneman, O. Sibony, C. Sunstein. Noise: A Flaw in Human Judgment, William Collins (2021)
[27] I.E. Dror. Cognitive and human factors in expert decision making: six fallacies and the eight sources of bias, Anal. Chem., 92 (12) (2020), pp. 7998-8004
[28] J. Kukucka, S.M. Kassin, P.A. Zapf, I.E. Dror. Cognitive bias and blindness: a global survey of forensic science examiners, Journal of Applied Research in Memory and Cognition, 6 (2017), pp. 452-459
[29] I.E. Dror. The paradox of human expertise: why experts get it wrong, N. Kapur (Ed.), The Paradoxical Brain, Cambridge University Press, Cambridge, UK (2011), pp. 177-188
[30] C. Eeden, C. De Poot, P. Koppen. The forensic confirmation bias: a comparison between experts and novices, J. Forensic Sci., 64 (1) (2019), pp. 120-126
[31] C. Huang, R. Bull. Applying Hierarchy of Expert Performance (HEP) to investigative interview evaluation: strengths, challenges and future directions, Psychiatr. Psychol. Law, 28 (2021)
[32] C. MacLean, I.E. Dror. The effect of contextual information on professional judgment: reliability and biasability of expert workplace safety inspectors,J. Saf. Res., 77 (2021), pp. 13-22
[33] E. Rassin. Anyone who commits such a cruel crime, must be criminally irresponsible’: context effects in forensic psychological assessment, Psychiatr. Psychol. Law (2021)
[34] V. Meterko, G. Cooper. Cognitive biases in criminal case evaluation: a review of the research, J. Police Crim. Psychol. (2021)
[35] C. FitzGerald, S. Hurst. Implicit bias in healthcare professionals: a systematic review, BMC Med. Ethics, 18 (2017), pp. 1-18
[36] M.K. Goyal, N. Kuppermann, S.D. Cleary, S.J. Teach, J.M. Chamberlain. Racial disparities in pain management of children with appendicitis in emergency departments, JAMA Pediatr, 169 (11) (2015), pp. 996-1002
[37] I.E. Dror. Biases in forensic experts, Science, 360 (6386) (2018), p. 243
[38] S.M. Kassin, I.E. Dror, J. Kukucka. The forensic confirmation bias: problems, perspectives, and proposed solutions, Journal of Applied Research in Memory and Cognition, 2 (1) (2013), pp. 42-52
[39] NAS. National Research Council, Strengthening Forensic Science in the United States: a Path Forward, National Academy of Sciences (2009)
[40] PCAST, President’s Council of Advisors on science and Technology (PCAST), Report to the President – Forensic Science in Criminal Courts: Ensuring Validity of Feature-Comparison Methods, Office of Science and Technology, Washington, DC (2016)
[41] NCFS, National Commission on Forensic Science. Ensuring that Forensic Analysis Is Based upon Task-Relevant Information, National Commission on Forensic Science, Washington, DC (2016)
[42] Forensic Science Regulator. Cognitive bias effects relevant to forensic science examinations, disponible sur https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/914259/217_FSR-G-217_Cognitive_bias_appendix_Issue_2.pdf
[43] ANZPAA, A Review of Contextual Bias in Forensic Science and its Potential Legal Implication, Australia New Zealand Policing Advisory Agency (2010)
[44] J. Kukucka, I.E. Dror. Human factors in forensic science: psychological causes of bias and error, D. DeMatteo, K.C. Scherr (Eds.), The Oxford Handbook of Psychology and Law, Oxford University Press, New York (2021)
[45] I.E. Dror, J. Melinek, J.L. Arden, J. Kukucka, S. Hawkins, J. Carter, D.S. Atherton. Cognitive bias in forensic pathology decisions, J. Forensic Sci., 66 (4) (2021)
[46] N. Sunde, I.E. Dror. A hierarchy of expert performance (HEP) applied to digital forensics: reliability and biasability in digital forensics decision making, Forensic Sci. Int.: Digit. Invest., 37 (2021)
[47] D.C. Murrie, M.T. Boccaccini, L.A. Guarnera, K.A. Rufino. Are forensic experts biased by the side that retained them? Psychol. Sci., 24 (10) (2013), pp. 1889-1897
[48] G. Langenburg. Addressing potential observer effects in forensic science: a perspective from a forensic scientist who uses linear sequential unmasking techniques, Aust. J. Forensic Sci., 49 (2017), pp. 548-563
[49] C.M. Thomas, E. Bertram, D. Johnson. The SBAR communication technique, Nurse Educat., 34 (4) (2009), pp. 176-180
[50] I. Wacogne, V. Diwakar. Handover and note-keeping: the SBAR approach, Clin. Risk, 16 (5) (2010), pp. 173-175
[51] M.A. Almazrouei, I.E. Dror, R. Morgan. The forensic disclosure model: what should be disclosed to, and by, forensic experts?, International Journal of Law, Crime and Justice, 59 (2019)
[52] I.E. Dror. Combating bias: the next step in fighting cognitive and psychological contamination, J. Forensic Sci., 57 (1) (2012), pp. 276-277
[53] D. Simon, Minimizing Error and Bias in Death Investigations, vol. 49, Seton Hall Law Rev. (2018), pp. 255-305
[54] CNN. Medical examiner: I “intentionally chose not” to view videos of Floyd’s death before conducting autopsy, April 9, 2021, disponible sur https://edition.cnn.com/us/live-news/derek-chauvin-trial-04-09-21/h_03cda59afac6532a0fb8ed48244e44a0 (2011)

Two cold cases solved through familial DNA searching ?

7 December 2024Newsavancés scientifiques, cold case, génétique, investigationadmin

As in the Élodie Kulik case in 2011 and that of the “Prédateur des bois” in 2022, two casefiles reopened by the Cold Case Unit in Nanterre are now close to being solved thanks to familial DNA searching,

“They say you’re only betrayed by your own,” a proverb that takes on its full meaning here. Two murders committed twelve years apart and seemingly unrelated have now been traced back to one and the same suspect—thanks to a genetic link established between members of the same family.

In 1988, fifteen-year-old Valérie Boyer was found with her throat slit along the railway tracks in Saint-Quentin-Fallavier. In 2000, forty-year-old Laïla Afif was shot dead in the head in La Verpillière. The only common factor between the two crimes was geographical proximity, as both occurred in neighboring towns in the Isère department. Lacking solid leads or similarities in the modus operandi, the investigations soon came to a standstill—until March 2024. More than twenty years later, the Cold Case Unit, created in 2022, reopened the Laïla Afif case and ordered new DNA analyses on samples recovered from the crime scene.

Proof through familial DNA

These forensic analyses, extended through the use of familial DNA searching, led investigators to identify, within the National Automated DNA Database (Fichier National Automatisé des Empreintes Génétiques – FNAEG), an individual previously implicated in another case whose DNA showed a 50% genetic match with the profile obtained in the Afif case. And as the immutable laws of genetics dictate—each person shares half of their genome with their biological parents and children—the investigators logically traced the lead back to the man’s father. Betrayed by his son’s DNA, Mohammed C. has now been indicted not only for the murder of Laïla Afif, but also for that of Valérie Boyer, as the reopened investigation revealed striking connections between the two crimes. The latter case is part of the notorious “Disparus de l’Isère” (the Isère disappearances) series, a string of disappearances that made national headlines in the 1980s and is already under review by the Cold Case Unit.

Further reading: COLD CASES UN MAGISTRAT ENQUÊTE (Cold Cases – A Magistrate Investigates), by Jacques Dallest

Criminal history is marked by sordid murders, brutal killings, mysterious disappearances, and puzzling suicides. Mysterious and puzzling because these cases have never been solved—the perpetrators never identified, the culprits never convicted. In proper French, these cases are referred to as “cold cases.” They number in the dozens and are often unknown to the general public. Only a few major unsolved cases have found their place in the annals of judicial history and continue to fuel debate and speculation: the Bruay-en-Artois case, the Fontanet case, the Grégory case, the Boulin case, and, more recently, the Chevaline shootings. But what exactly is a cold case? What does this English term signify within the context of the French judicial system? Should these cases be reopened? And after so many years, how can justice still be served? In this scholarly and meticulously documented essay, Jacques Dallest—former investigating judge, public prosecutor, and Advocate General—offers a comprehensive analysis of the issue as no book has ever done before.

Order online.

Cold case investigations : defeatists and careless, beware !

28 April 2024Articles, Justice, Major criminal casescold case, investigationadmin

A seasoned investigator deeply committed to solving cold cases, Raphael Nedilko describes them as “an equation with three unknowns: a complex case file, a family in total incomprehension, and an institution that remains largely deaf despite obvious goodwill at the individual level.”[1]

This is a perfect summary of an issue that continues to raise questions today. Victims and the justice system too often maintain relations as difficult as the case itself. The former cannot understand the inability to solve the crime or the disappearance and perceive only unjustifiable shortcomings. Overwhelmed by massive and urgent litigation, the latter recognizes its inability to devote time to old cases—serious, yes, but moribund in its eyes. It will invoke a lack of resources and an initial, fruitless investigation that would be pointless to reopen.

But what of the investigation that gave rise to the scandal? Is it not itself at fault, plunging families into despair and indignation? And does reopening or relaunching a case require a different treatment from an investigation that, by definition, concerns past events?

The initial criminal investigation: rigor is essential

It is often repeated in police academies and at the National School for the Judiciary (ENM): everything depends on the quality of the initial investigation. Truth lies in the rigor of crime scene observations and evidence collection procedures. These tasks are numerous and sometimes delicate, depending on the configuration of the crime scene. Three scenarios arise, from the simplest to the most complex:

• The crime scene is located in an enclosed space—house, apartment, or their outbuildings. The homicide has clearly taken place there and the victim’s body is present. The perimeter is easy to secure, greatly facilitating the investigators’ work. However, a risk remains: third parties (relatives, neighbors, emergency services, etc.) may have entered the premises before the investigators’ arrival, potentially contaminating the crime scene.

• The crime scene is in a public place. The victim has been killed in the street or in a vehicle (settling of scores). The perimeter is more uncertain and less easily secured, inevitably complicating the search for traces and evidence. The presence of bystanders may also interfere with the investigation. In addition, the event may generate public disorder, particularly if it occurs in a neighborhood prone to urban violence.

• The crime scene is uncertain or ill-defined. This is the most delicate situation for investigators. The body is discovered in a natural environment—forest, woods, dirt path, or aquatic setting such as a river, pond, or the sea. Defining the crime scene may be complex, if not impossible (e.g., an immersed body). Moreover, the presence of the body does not necessarily mean the murder took place where it was found. It is likely that the crime occurred elsewhere and that the perpetrators sought to dispose of the victim. This configuration makes the investigation particularly challenging, especially if the death occurred long ago.

The layout of the crime scene thus directly affects the conduct of the investigation. In any case, the investigative service must display the utmost rigor. It is well known that initial observations are decisive: any omission, oversight, or negligence will weigh heavily on the case. Establishing the truth may be compromised, with errors often proving irreversible.

The uncertainty surrounding the cause of death can also arise. It may be natural, accidental, criminal, or suicidal. Determining the cause ab initio is not always simple. An erroneous initial assessment can gravely distort the reasoning of both investigators and prosecutors. Mistaking a homicide for a suicide—or the reverse—can cause irreparable deficiencies or, conversely, unnecessary and time-consuming actions, whereas prompt investigations are crucial for preserving evidence.

“Solving a murder is a priority task that requires perfect coordination between investigators and magistrates.”
Jacques DALLEST

Careful observation of the location where the body is discovered, thorough and rigorous documentation, preservation of traces and evidence, meticulous collection, and methodical conservation—these are the fundamental recommendations that first responders must respect.

Unfortunately, insufficient staffing, inadequate training, poor equipment, culpable negligence, serious mistakes, and dangerous certainties all hinder the investigation. An incomplete neighborhood canvass, overly hasty interviews, unexecuted searches, and missing verifications likewise contribute to failures that seriously undermine the inquiry.

Magistrates must fully exercise their prerogatives in directing the investigation. The prosecutor involved at the outset and the investigating judge subsequently assigned to the case both play a fundamental role. The absence of precise directives for investigators, or a lack of diligence in case supervision, cannot be justified by an excessive workload. Admittedly, the criminal magistrate is above all a generalist, overwhelmed by urgent cases and daily pressures. However, criminal cases—particularly crimes involving loss of life—demand complete commitment and particular attention to the investigations conducted by the assigned service. Solving a murder is a priority task that requires perfect coordination between investigators and magistrates.

This necessary professional rigor must also account for the expectations of the victim’s relatives, devastated by a terrible tragedy and in deep distress. Distraught, they turn to justice, hoping for attention that is too often insufficient, if not absent. Even when acting as civil parties, they unanimously complain of being kept in the dark regarding the progress of the investigation—and worse, of not being received or heard by the investigating judge. Let us recall that Article 90-1 of the Code of Criminal Procedure obliges the judge to inform the civil party every six months on the progress of the investigation. The same text also allows relatives to be heard by the judge every four months upon their express request.

Sadly, these provisions are often forgotten. Civil party lawyers must insist on their strict application and act proactively in this regard. Too few actually use the rights granted to them by law, instead waiting passively for the investigating judge to summon them. This is most regrettable.

Is the judicial treatment fundamentally different when the crime remains unsolved? What means do investigators and the judiciary have at their disposal to pursue such cases—old, yes, but still profoundly painful for the relatives?

Cold case investigations: determination and empathy required

Reopening an old criminal investigation is a delicate task, all the more so when the facts remain unsolved. Past missteps weigh heavily on those tasked with solving the mystery. Forgotten witnesses, overlooked searches, neglected seizures, technical inquiries left aside, ill-suited strategies, and lack of commitment all lead to a dead end—an impasse from which it is difficult to escape. How many mishandled cases have resulted in perpetrators going unpunished? And how many murderers or rapists were able to reoffend simply because they were never identified?

The creation of the Specialized Unit for Serial and Unsolved Crimes (PCSNE), established within the Nanterre Judicial Court on 1 March 2022, has reshuffled the deck. Now, with the new criminal provisions introduced by the Law of 22 December 2021 (Title XXV bis, as incorporated into the Code of Criminal Procedure), the judicial handling of cold cases has gained a momentum that many hope will prove decisive.

The Nanterre Unit now has jurisdiction over violent and sexual crimes (murder, rape), as well as abductions and unlawful confinements committed—or likely committed—repeatedly, at different times, by the same individual against different victims, and more generally, over crimes whose perpetrator has not been identified more than eighteen months after their commission (Article 706-106-1).

Serial crimes and unsolved crimes are thus to be referred to Nanterre, regardless of where they were committed within French territory.

This represents a major step forward—long demanded by victims’ families—which helps restore their hope in justice. Composed of motivated, specialized prosecutors and investigating judges, the Nanterre Unit devotes all its energy to the exclusive handling of cold cases, thereby opening up new prospects for resolution. It is well known that, overwhelmed by urgent criminal matters and mass litigation, generalist magistrates can devote only limited time to old cases, however serious they may be. The first years of the Unit’s operation, and several notable successes, have demonstrated the value of a justice system focused on this highly specific area.

“At the same time, Prosecutors General and Public Prosecutors will have to establish a genuine criminal memory enabling them to know and monitor unsolved cases within their jurisdiction.”
Jacques DALLEST

A genuine “cold case culture,” born of the new law, must now permeate the judiciary. It is already clear that the Nanterre Unit will not have the material capacity to centralize all unsolved crimes in France, some of which date back more than forty years. It is therefore imperative that all Public Prosecutors and investigating judges handling criminal cases fully embrace this new and virtuous dynamic.

Taking genuine interest in these cases, developing tailored investigative methodologies, making use of modern investigative tools (such as artificial intelligence), mastering and applying new scientific disciplines (forensic sciences), reaching out to civil parties and listening to them, learning how to question suspects (behavioral analysis can assist here), forging links with foreign partners where necessary, and working with the media when appropriate—these are all avenues of effort that must guide magistrates in charge of cold cases.

*Cold Cases – An Investigating Magistrate’s Inquiry – Jacques DALLEST – Mareuil Editions*

At the same time, Prosecutors General and Public Prosecutors will have to establish a genuine criminal memory, enabling them to know and monitor unsolved cases within their jurisdiction. This memory is largely absent in prosecutors’ offices. Upon taking office, a prosecutor will not find on his or her computer a list of unsolved criminal cases, whether ongoing or closed.

Five tables should be regularly updated in the 91 prosecutors’ offices with a criminal division (out of 164 jurisdictions): murders against persons unknown, rapes against persons unknown, abductions and unlawful confinements against persons unknown, discoveries of unidentified bodies (including those buried under the designation “X”), and missing persons cases of concern. These tables would be communicated to the Prosecutor General (36 in France), who would periodically organize evaluation and monitoring meetings with the relevant prosecutors. A pooling of such data and exchanges could also be organized at the interregional level (several courts of appeal), so that each office has a panoramic view of crimes and disappearances recorded across this wider territory. Who can seriously believe that a criminal limits his actions to a single jurisdiction?

A criminal memory is indispensable to better identify violent and sexual crime, to address it with greater determination, to respond usefully to the expectations of relatives and their lawyers, and to be able to face media inquiries.

“One does not question a suspected murderer, possibly serial, in the same way as one questions a drug trafficker or a burglar.”
Jacques DALLEST

Seriously investigating a cold case also requires following these recommendations:

• Never destroy the case evidence, even if the case has been closed. A recent provision, effective 30 September 2024, prohibits any destruction within ten years after the expiry of the statute of limitations, i.e. thirty years after the case has been closed. Criminal evidence must be stored in a dedicated space, preserved in good condition, and carefully tracked. Losing a piece of evidence through negligence is unacceptable, as it may eliminate any chance of success.

• Give special attention to the victim’s relatives, the civil parties: receive them regularly, listen to them, carry out the acts they request, explain the progress and prospects of the case, and treat them simply with dignity. As Raphael Nedilko rightly says, it is a matter of honesty, honor, and humanity.

• Know how to conduct (or re-conduct) witness interviews, which can prove decisive. A sound methodology for collecting testimony is essential. The same applies to suspect interviews: one does not question a suspected murderer, possibly serial, in the same way as a drug trafficker or a burglar.

• Re-examine the work already carried out, not to criticize it as a matter of principle, but to identify shortcomings or omissions.

• Draw connections with similar cases or those showing converging elements. The notion of a “criminal signature” must be set aside: many serial criminals in France act without a consistent modus operandi. The fact that victims differ in age or gender, or that the weapon used to kill them is not the same, does not exclude the possibility of a single perpetrator. Beware of the limits of American-style profiling, which can lead to serious errors.

• Remain constantly informed about scientific advances, which are in perpetual evolution. DNA analysis today is far removed from what it was at its discovery, and the exploitation and evidentiary value of genetic traces will advance considerably in the decades to come.

• Do not rely solely on scientific evidence, which may be lacking. Traditional investigation, with its human dimension, remains indispensable. Commissaire Maigret has not ceded his place to the hard sciences researcher.

• Train in new investigative techniques—digital, computer, telephonic, ballistic, etc.

• Beware of certainties, biases, and preconceived ideas, which lead to tunnel vision from which there is no escape. Excessive self-confidence generates errors that are often irreparable.

• Work not only for the establishment of truth but also for posterity. Other investigators may one day take over. One must ensure not to leave them unable to move forward. Humility is a virtue here, more necessary than ever.

• Never give up, for scientific progress may one day allow the case to be solved. Determination is as necessary as teamwork.

The judicial handling of cold cases is long, uncertain, and demanding. Hope keeps families alive. It must also guide the actors in the case. The investigating judge in charge and the investigators must speak to one another, exchange views, and set objectives. The lawyer for the civil parties—their guide through the judicial maze—cannot be sidelined as if he were an unwelcome figure. He has his rightful place in the proceedings, and his active contribution is required. More than anywhere else, collective intelligence is called upon here. qu’ailleurs, l’intelligence collective est convoquée.

“Man, no one has plumbed the depths of your abysses,” wrote Baudelaire. To attempt it—what greater endeavor could there be?

_{[1]See his article “Cold Cases: Let Us Give Hope a Chance,” in issue no. 52 of Cahiers de la Sécurité et de la Justice (2021), “Les crimes complexes, cold cases, meurtres sériels, disparitions non élucidées.” See also his excellent book L’obstiné (Studiofact Editions, 2023).}