Machine learning algorithms in forensic science: A response to Morrison et al. (2022)

In Swofford & Champod (2022), we report the results of semi-structured interviews to various criminal justice stakeholders, including laboratory managers, prosecutors, defense attorneys, judges, and other academic scholars, on issues related to interpretation and reporting practices and the use of computational algorithms in forensic science within the American criminal justice system. Morrison et al. (2022) responded to that article claiming the interview protocol used a leading question with a false premise relating to the opaqueness of machine-learning methods. We disagree with the assertions of Morrison et al. (2022) and contend the premise to the question was relevant and appropriate

Finding the way forward for forensic science in the US:a commentary on the PCAST report

A recent report by the US President’s Council of Advisors on Science and Technology (PCAST) [1] has made a number of recommendations for the future development of forensic science. Whereas we all agree that there is much need for change, we find that the PCAST report recommendations are founded on serious misunderstandings. We explain the traditional forensic paradigms of match and identification and the more recent foundation of the logical approach to evidence evaluation. This forms the groundwork for exposing many sources of confusion in the PCAST report. We explain how the notion of treating the scientist as a black box and the assignment of evidential weight through error rates is overly restrictive and misconceived. Our own view sees inferential logic, the development of calibrated knowledge and understanding of scientists as the core of the advance of the profession

Estimating the quantity of transferred DNA in primary and secondary transfers.

We conducted experiments to characterize the quantity of DNA recovered on surfaces using 6 donors with a view to help assigning probabilities to the observation of given quantities of DNA under different transfer scenarios. The donors were asked to conduct a total of 120 simulations involving primary transfer on a knife handle. With 2 selected donors, 60 associated experiments involving secondary transfer were also carried out. DNA recovered on COPAN’s FLOQSwab™ was extracted, quantified and profiled using standard commercial kits. DNA mixtures were subsequently deconvoluted using STRmix™ to obtain the proportion corresponding to the person of interest (POI). The transfer proportion between the quantity of DNA on the bare hands and the amounts recovered on the touched surfaces was also measured and studied. For a given activity, each donor left varying amounts of DNA amounting to distributions that can be characterized by their means and standard deviations. The quantity of transferred DNA is dependent on the donor and on the type of transfer. Typically, our “best” donor left an average of 0.84ng (SD = 1.23) on a knife handle compared to a mean of 0.07ng (SD = 0.09) for the least “prone to leave DNA” donor. For secondary transfer, we recorded a mean of 0.04ng (SD = 0.11) for the first donor and of 0.002 (SD = 0.01, max = 0.04ng) for the second. Linked to the above is the observation that the transfer proportion (i.e. the ratio of the quantity of DNA on an hand to the amount of DNA recovered following a transfer) depends also on the donor and on the type of the transfer. Hence the amount of DNA obtained on a given touched surface cannot simply be deduced from the quantity of DNA available on a donor’s hand. Given these sources of variability, it is not advised to use a single and fixed label, such as “good “or “bad” regardless of the circumstances, to describe a donor’s ability to leave DNA. To properly evaluate the probability of finding a given quantity of DNA the whole variation of DNA quantity should be accounted for. This can be done by using or measuring empirically the appropriate underpinning distribution for that quantity. Note however that it will be conditioned upon the donor, the receiving surface and the transfer mechanism. We also explored the potential benefit of deconvoluting mixtures to better characterize the quantity of DNA left by the POI as opposed to the total quantity of DNA measured by quantification. Our results show that such deconvolution is beneficial when low quantities of POI’s DNA may be mixed with larger quantities such as in secondary transfer scenarios. For primary transfers on clean surfaces, the touching person will dominate in the recovered DNA and the deconvolution is not critical

Nanoparticles for fingermark detection: An insight into the reaction mechanism

© 2014 IOP Publishing Ltd. This publication presents one of the first uses of silicon oxide nanoparticles to detect fingermarks. The study is not confined to showing successful detection of fingermarks, but is focused on understanding the mechanisms involved in the fingermark detection process. To gain such an understanding, various chemical groups are grafted onto the nanoparticle surface, and parameters such as the pH of the solutions or zeta potential are varied to study their influence on the detection. An electrostatic interaction has been the generally accepted hypothesis of interaction between nanoparticles and fingermarks, but the results of this research challenge that hypothesis, showing that the interaction is chemically driven. Carboxyl groups grafted onto the nanoparticle surfaces react with amine groups of the fingermark secretion. This formation of amide linkage between carboxyl and amine groups has further been favoured by catalyzing the reaction with a compound of diimide type. The research strategy adopted here ought to be applicable to all detection techniques using nanoparticles. For most of them the nature of the interaction remains poorly understood

Les nouvelles lignes directrices du European Network of Forensic Sciences Institut en matière d’évaluation et de communication des résultats d’analyses et d’expertises scientifiques

Au printemps 2015, le European Network of Forensic Science Institutes a publié des lignes directrices visant à unifier les méthodes de travail des scientifiques agissant comme auxiliaires de la justice, plus précisément l’évaluation des résultats d’analyses scientifiques (logique du raisonnement) et la communication de ces résultats aux magistrats. Cette contribution a pour but d’expliciter ces lignes directrices et d’expliquer en quoi il est primordial que la justice suisse les adopte. — Im Frühjahr 2015 publizierte das ENFSI (European Network of Forensic Science Institutes) Leitlinien für die Vereinheitlichung wissenschaftlicher Arbeitsmethoden, insbesondere für Bewertung von wissenschaftlichen Untersuchungsergebnissen (Logik der Befundbewertung) und die Berichterstattung zuhanden der Justiz. Dieser Beitrag erläutert diese Richtlinien und erklärt, weshalb es wichtig ist, dass sie in die Schweizer Justizpraxis Eingang finden

Evaluation of Forensic DNA Traces When Propositions of Interest Relate to Activities : Analysis and Discussion of Recurrent Concerns

When forensic scientists evaluate and report on the probative strength of single DNA traces, they commonly rely on only one number, expressing the rarity of the DNA profile in the population of interest. This is so because the focus is on propositions regarding the source of the recovered trace material, such as “the person of interest is the source of the crime stain.” In particular, when the alternative proposition is “an unknown person is the source of the crime stain,” one is directed to think about the rarity of the profile. However, in the era of DNA profiling technology capable of producing results from small quantities of trace material (i.e., non-visible staining) that is subject to easy and ubiquitous modes of transfer, the issue of source is becoming less central, to the point that it is often not contested. There is now a shift from the question “whose DNA is this?” to the question “how did it get there?” As a consequence, recipients of expert information are now very much in need of assistance with the evaluation of the meaning and probative strength of DNA profiling results when the competing propositions of interest refer to different activities. This need is widely demonstrated in day-to-day forensic practice and is also voiced in specialized literature. Yet many forensic scientists remain reluctant to assess their results given propositions that relate to different activities. Some scientists consider evaluations beyond the issue of source as being overly speculative, because of the lack of relevant data and knowledge regarding phenomena and mechanisms of transfer, persistence and background of DNA. Similarly, encouragements to deal with these activity issues, expressed in a recently released European guideline on evaluative reporting (Willis et al., 2015), which highlights the need for rethinking current practice, are sometimes viewed skeptically or are not considered feasible. In this discussion paper, we select and discuss recurrent skeptical views brought to our attention, as well as some of the alternative solutions that have been suggested. We will argue that the way forward is to address now, rather than later, the challenges associated with the evaluation of DNA results (from small quantities of trace material) in light of different activities to prevent them being misrepresented in court