title: The evaluation of evidence relating to traces of cocaine on banknotes.
abstract: Banknotes can be seized from crime scenes as evidence for suspected association with illicit drug dealing. Tandem mass spectrometry data are available from banknotes seized in criminal investigations, as well as from banknotes from general circulation. The aim of the research is to evaluate the support provided by the data gathered in a criminal investigation for the proposition that the banknotes from which the data were obtained are associated with a person who is associated with a criminal activity related to cocaine in contrast to the proposition that the banknotes are associated with a person who is not associated with a criminal activity involving cocaine. The data considered are the peak area for the ion count for cocaine product ion m/z 105. Previous methods for assessment of the relative support for these propositions were concerned with the percentage of banknotes contaminated or assume independence of measurements of quantities between adjacent banknotes. Methods which account for an association of the quantity of drug on a banknote with that on adjacent banknotes are described. The methods are based on an autoregressive model of order one and on two versions of a nonparametric approach. The results are compared with a standard model which assumes measurements on individual banknotes are independent; there is no autocorrelation. Performance is assessed using rates of misleading evidence and a recommendation made as to which method to use.
authors: School of Mathematics and Maxwell Institute, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom.
authors: Amy
authors: A
authors: Wilson
authors: School of Mathematics and Maxwell Institute, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom. Electronic address: c.g.g.aitken@ed.ac.uk.
authors: Colin
authors: C
authors: Aitken
authors: Mass Spec Analytical Ltd., Building 20F, Golf Course Lane, Bristol BS34 7RP, United Kingdom.
authors: Richard
authors: R
authors: Sleeman
authors: Clinical and Statewide Services Division, Queensland Health, PO Box 594, Archerfield, Queensland 4108, Australia.
authors: James
authors: J
authors: Carter
keywords: Autoregressive model; Banknotes; Cocaine; Evidence evaluation; Likelihood ratio; Nonparametric density estimation