title: Lead isotope ratios for bullets, forensic evaluation in a Bayesian paradigm.
abstract: Forensic science is a discipline concerned with collection, examination and evaluation of physical evidence related to criminal cases. The results from the activities of the forensic scientist may ultimately be presented to the court in such a way that the triers of fact understand the implications of the data. Forensic science has been, and still is, driven by development of new technology, and in the last two decades evaluation of evidence based on logical reasoning and Bayesian statistic has reached some level of general acceptance within the forensic community. Tracing of lead fragments of unknown origin to a given source of ammunition is a task that might be of interest for the Court. Use of data from lead isotope ratios analysis interpreted within a Bayesian framework has shown to be suitable method to guide the Court to draw their conclusion for such task. In this work we have used isotopic composition of lead from small arms projectiles (cal. .22) and developed an approach based on Bayesian statistics and likelihood ratio calculation. The likelihood ratio is a single quantity that provides a measure of the value of evidence that can be used in the deliberation of the court.
authors.affiliation: University of Oslo, Department of Geosciences, Norway; National Criminal Investigation Service (KRIPOS), P.O. Box 8163, dep, 0034 Oslo, Norway. Electronic address: knut.endre.sjastad@politiet.no.
authors.forename: Knut-Endre
authors.initials: KE
authors.lastname: Sjåstad
authors.affiliation: Lancaster University, Department of Mathematics and Statistics, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Lucy
authors.affiliation: University of Oslo, Department of Geosciences, Norway.
authors.forename: Tom
authors.initials: T
authors.lastname: Andersen
keywords: Ammunition; Bayesian statistics; Bullets; Descriptive statistics; Forensic evaluation; Interpretation; LR; Lead isotope ratios; Lead isotopic composition (LIC); Likelihood ratio; Multicollector inductive coupled plasma mass spectrometry (MC-ICP-MS)