Technical note: Proposed method to objectively evaluate gunshot residue comparisons does not generalize to different-location settings

Forensic Science International, vol. 369, pp. 112414

Abstract

Previously, we proposed a likelihood ratio system for pairwise source comparison of gunshot residue (GSR) samples based on elemental composition. Only pairs of GSR samples from the same location type (e.g., hand-hand) were considered, as the data originates from casework and ground truth is not available for samples from different location types (e.g., hand-cartridge case). This lack of sample pairs taken from different locations is a limitation, as casework will usually require such sample pairs to be evaluated. In this study, we test the impact of this sampling location limitation by evaluating the model with an experimental dataset for which ground truth was available for same-location as well as different-location pairs. We find a sharp decline in the performance of the model, with C llr deteriorating from 0.35 to 0.98. Additional exploration of various system extensions does not lead to significant improvements. We discuss the potential causes for this decline and conclude the system is not currently ready for application in forensic casework. • We validate an LR system for forensic source comparison of gunshot residue samples. • We find that performance drops to near random for different-location comparisons. • We conclude that the LR system is not currently ready for application in casework.

Authors 7

1. Kim de Bie

   Netherlands Forensic Institute

   Affiliation as printed

   Netherlands Forensic Institute, Laan van Ypenburg 6, The Hague 2497 GB, the Netherlands

2. Marieke Vinkenoog corresponding Aachen

   Leiden University · Netherlands Forensic Institute

   Affiliation as printed

   Netherlands Forensic Institute, Laan van Ypenburg 6, The Hague 2497 GB, the Netherlands; Leiden University, Rapenburg 70, Leiden 2311 EZ, the Netherlands. Electronic address: m.vinkenoog@liacs.leidenuniv.nl

3. Simone Ariëns

   Netherlands Forensic Institute

   Affiliation as printed

   Netherlands Forensic Institute, Laan van Ypenburg 6, The Hague 2497 GB, the Netherlands

4. T.L. Dirkse

   Netherlands Forensic Institute

   Affiliation as printed

   Netherlands Forensic Institute, Laan van Ypenburg 6, The Hague 2497 GB, the Netherlands

5. Corina Kukurin

   Netherlands Forensic Institute

   Affiliation as printed

   Netherlands Forensic Institute, Laan van Ypenburg 6, The Hague 2497 GB, the Netherlands

6. Wauter Bosma

   Netherlands Forensic Institute

   Affiliation as printed

   Netherlands Forensic Institute, Laan van Ypenburg 6, The Hague 2497 GB, the Netherlands

7. Rolf J.F. Ypma

   Netherlands Forensic Institute

   Affiliation as printed

   Netherlands Forensic Institute, Laan van Ypenburg 6, The Hague 2497 GB, the Netherlands