ARSON, STATISTICS AND THE LAW - CAN THE DEFENDANTS PROXIMITY TO A LARGE NUMBER OF FIRES BE EXPLAINED BY CHANCE

The statistical evidence which played a major part in a case of arson in Norway is presented as a case study. A fireman was known to have been present at the scenes of fire in the hours prior to their onset in no less than 24 out of 37 cases of forest fire. The study, through probabilistic analysis, attempts to throw light on whether this was so strikingly often that he had to be the arsonist, carefully taking into account special features that could explain the peculiar behaviour of the defendant. The conclusion hinged on certain input parameters to the calculation, and the principal aim of the work was to organize, structure and reduce the material to a few quantities that were easier to comprehend than the problem in its original form. The court accepted the relevance of the calculations, and used it against the defendant, but he was still acquitted. A number of issues related to probabilistic interpretation of evidence are discussed.