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.
Forensic DNA Trace Evidence Interpretation: Activity Level Propositions and Likelihood Ratios provides all foundational information required for a reader to understand the practice of evaluating forensic biology evidence given activity level propositions and to implement the practice into active casework within a forensic institution. The book begins by explaining basic concepts and foundational theory, pulling together research and studies that have accumulated in forensic journal literature over the last 20 years.The book explains the laws of probability - showing how they can be used to derive, from first principles, the likelihood ratio - used throughout the book to express the strength of evidence for any evaluation. Concepts such as the hierarchy of propositions, the difference between experts working in an investigative or evaluative mode and the practice of case assessment and interpretation are explained to provide the reader with a broad grounding in the topics that are important to understanding evaluation of evidence. Activity level evaluations are discussed in relation to biological material transferred from one object to another, the ability for biological material to persist on an item for a period of time or through an event, the ability to recover the biological material from the object when sampled for forensic testing and the expectations of the prevalence of biological material on objects in our environment. These concepts of transfer, persistence, prevalence and recovery are discussed in detail in addition to the factors that affect each of them.The authors go on to explain the evaluation process: how to structure case information and formulate propositions. This includes how a likelihood ratio formula can be derived to evaluate the forensic findings, introducing Bayesian networks and explaining what they represent and how they can be used in evaluations and showing how evaluation can be tested for robustness. Using these tools, the authors also demonstrate the ways that the methods used in activity level evaluations are applied to questions about body fluids. There are also chapters dedicated to reporting of results and implementation of activity level evaluation in a working forensic laboratory. Throughout the book, four cases are used as examples to demonstrate how to relate the theory to practice and detail how laboratories can integrate and implement activity level evaluation into their active casework.
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In this case study, we want to gain insights into how residents of three municipalities communicate about the new murder scenario of the cold case of Marianne Vaatstra and the possibility of a large-scale DNA familial searching. We investigate how stakeholders shape their arguments in conversation with each other and with the police. We investigate the repertoires that participants use to achieve certain effects in their interactions with others in three focus groups. The results show that the analyzed repertoires are strong normative orientated. We see two aspects emerge that affect the support for large-scale DNA familial searching. These are: 1. Cautious formulations: respondents showed restraint in making personal judgments and often formulated these on behalf of others. Participants would not fully express themselves, but adjusted to what seemed the socially desirable course. 2. Collective identity: respondents focused on the similarities between themselves and the needs, interests, and goals of other participants. Participants also tried in a discursive way to convince each other to participate in the large-scale familial searching. These two major discursive activities offered the communication discipline guidance for interventions into the subsequent communication strategy.
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