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The transfer, persistence and secondary transfer of gunshot residue (GSR): Implications for crime reconstruction and forensic protocol studied using Bayesian modelling

7 March 2012

James French

Research into the secondary transfer of forensic particulates highlighted how evidence can be transferred to innocent individuals via intermediaries. Further work could assist in the interpretation of trace physical evidence and its presentation in court; informing and improving the accuracy of conclusions and ultimately assisting in the exoneration/exclusion of innocent parties, the implication/conviction of offenders, and the provision of safe justice. 

Bayesian networks are increasingly employed when dealing with uncertainty in bodies of forensic evidence, particularly when multiple variables are present. They permit the testing of hypotheses about evidence in light of available information, which itself may be constantly updated. Repeatable experimental data on the rates of multiple transfer and persistence of gunshot residue (GSR) will be derived by experimental scenarios mimicking forensic contexts conducted with the Tactical Firearms Unit at Surrey Police HQ, Guildford, UK. Samples will be analysed and the GSR quantified using SEM-EDX and an automated analysis package, INCAGSR, in collaboration with Oxford Instruments, UK. Data will be then be combined in dynamic Bayesian networks, permitting assessment of the likelihood that a recovered sample could have originated via a secondary transfer. 

The research will contribute to the body of theory on trace evidence dynamics, while exploring the use of Bayesian probabilistic analysis in engendering a practical application of such theory. The novel combination of experimental and analytical techniques will unlock further investigative and probative value of GSR evidence.  Findings will be of interest in forensic science and legal spheres, and to practitioners in the investigation of firearms-related offences.