Tech Reports

ULCS-09-013

Evidential Reasoning about Motives: A Case Study

Floris Bex, Trevor Bench-Capon and Katie Atkinson

Abstract

Motives play an important role at every stage of a criminal investigation. They can be used to search for an explanation of the crime (why was this person killed?), to identify a suspect (who would have killed this person for this reason), and to persuade a jury of a suspect's guilt (this motive explains why this person committed this crime). We have previously developed an account of motivations based on a general approach to practical reasoning. In this paper we will concentrate on the use of motives to provide plausibility to a story intended to persuade a jury of a person's guilt or innocence. We will concentrate on a particular case study, formalised previously by Thagard, the two trials of Claus von Bulow. An advantage of our approach is that it allows stories to be considered from an intentional as well as a physical stance, whereas in previous accounts, including Thagard's, only the physical stance is available. We show how our approach can be used to explain the outcome of both trials, and to identify the points in which the defence could be improved from the first trial to the second.

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