In sexual assault cases, the retrieved DNA quantity and sampling location from the victim’s underwear may provide valuable information for activity level evaluative reporting. DNA can transfer from site to site on an exhibit, or be lost within packaging, complicating interpretation. Experiments are needed to investigate these factors. This preliminary study compared two cleaning methods to prepare undergarments for such experimentation: hand-washing with warm water and washing with bleach before rinsing. Results show a significantly lower quantity of DNA on washed underwear using both methods. Warm-water hand-washing, the more straightforward method, was selected for further experimentation.
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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