Fingermarks are highly relevant in criminal investigations for individualization purposes. In some cases, the question in court changes from ‘Who is the source of the fingermarks?’ to ‘How did the fingermark end up on the surface?’. In this paper, we explore evaluation of fingermarks given activity level propositions by using Bayesian networks. The variables that provide information on activity level questions for fingermarks are identified and their current state of knowledge with regards to fingermarks is discussed. We identified the variables transfer, persistency, recovery, background fingermarks, location of the fingermarks, direction of the fingermarks, the area of friction ridge skin that left the mark and pressure distortions as variables that may provide information on how a fingermark ended up on a surface. Using three case examples, we show how Bayesian networks can be used for the evaluation of fingermarks given activity level propositions.
Bayesian networks have shown to be a useful tool for the evaluation of forensic findings given activity level propositions. In this paper, we demonstrate how case specific experiments can be used to assign probabilities to the states of the nodes of a Bayesian network for the evaluation of fingermarks given activity level propositions. The transfer, persistence and recovery of fingermarks on knives is studied in experiments where a knife is either used to stab a victim or to cut food, representing the activities that were disputed in the case of the murder of Meredith Kercher. Two Bayesian networks are constructed, exploring the effect of different uses of the experimental data by assigning the probabilities based on the results of the experiments. The evaluation of the findings using the Bayesian networks demonstrates the potential for fingermarks in addressing activity level propositions.
Selecting the most successful and relevant traces at the crime scene is of the utmost importance as irrelevant traces may take up valuable capacity, increasing the risk that cases remain unsolved. In order to ensure that most relevant traces are collected, knowledge is required regarding how and where forensic traces are deposited given the activities being considered in the case relevant scenarios. As of now, however, this knowledge is limited. While studies on the transfer, prevalence, persistence and recovery of trace materials are becoming more common, most of such studies focus on crime centered scenarios and often do not take alternative, innocent, scenarios into account. Moreover, these studies often focus on specific objects or small spaces such as offices or vehicles. With the project No trace to waste (start: January 2023), we aim to extend the knowledge on trace dynamics as a strategy to improve the search for and selection of most relevant and successful traces. Throughout the project, the focus will be on DNA and fingermarks within home environments, as burglaries and home invasions remain common offenses and can be considered highly impactful on the victim’s lives. During the first phase, the distribution of traces given certain scenarios is investigated. Test subjects are asked to simulate various, both innocent and crime-related, activities within the model homes of the Dutch Police Academy. A fluorescent tracer is used to determine the objects/surfaces which the test subject has been in contact with and thus, where trace material could be expected to be deposited. Using these findings, the project moves onwards to investigate the persistence and transfer of actual traces during social settings, the prevalence of residents’ own DNA and fingermarks in the average active home and how these influence the recovery of crime-related traces post-offense. Finally, the project aims at supporting the forensic practitioners of the future. The knowledge obtained will be used to evaluate how to improve current practices and professional education. This in turn will support forensic practitioners on-scene with the selection of relevant traces and sampling locations and allows for a more efficient use of the available capacity and resources.
