Chapter 6Evaluation given crime level propositions

Chapter 3 introduced general elements concerning the construction and the evaluation of Bayesian networks for forensic inference problems. As in previous chapters, these ideas are extended here to a more systematic study of the evaluation of results of forensic examinations in various scientific disciplines. Particular attention is drawn to so-called transfer material (e.g. fibres and glass fragments), marks (e.g. shoemarks and firearms/toolmarks) and various types of transferable biological trace matter containing DNA. This chapter mainly focuses on the analysis and discussion of likelihood ratios that involve propositions at a hierarchical level known in the context as offence (or crime) level. Literature on the topic (e.g. Evett 1993; Stoney 1994) has considered such formulaic developments for cases in which material is found on a crime scene (or victim), sometimes referred to as offender to scene (or victim) transfer cases. These settings involve a single stain found on a crime scene, but with possible uncertainty about the degree to which that stain is relevant (i.e. uncertainty about whether or not the stain has been left by the offender). Extensions to multiple stains or multiple offenders have also been described (Garbolino and Taroni 2002). Yet, another variation of evaluative settings with propositions at crime level deals with potential transfer in the opposite direction, that is when material is collected on a person ...

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