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Automated interpretation of firearm mark comparison results

Published

Author(s)

Martin Baiker-Sørensen, Ivo Alberink, Laura Granell, Leen van der Ham, Erwin J.A.T. Mattijssen, Erich Smith, Johannes A. Soons, Peter Vergeer, Xiaoyu Alan Zheng

Abstract

In this article an automated approach for interpretation of firearm mark comparison results is presented. First, similarity scores are derived for marks typically encountered on primers of fired cartridge cases: aperture shear striations as well as breechface and firing pin impressions. Subsequently, these scores are interpreted with representative reference distributions of known matching (KM) and known non-matching (KNM) firearm pairs, in a common source likelihood ratio (LR) system. We study various alternatives to set up such an LR system and compare them using various qualitative and quantitative comparison criteria known from the literature. These are then used to determine the optimum system for a firearm-ammunition combination often encountered in casework, Glock firearms with nickel primer ammunition (Fiocchi). The system outputs an LR and a measure of LR uncertainty. In addition, the range of possible LR-values is limited to a minimum and maximum value in areas of the score domain, with little reference data. Finally, the possibility to combine LRs of individual mark interpretations into one LR for the entire primer is assessed. The results show that different approaches are optimal for different types of similarity scores. For the chosen firearm-ammunition combination, non-parametric kernel density estimation (KDE) models performed best for the cross correlation (CCF) and areal cross correlation (ACCF) scores, whereas parametric models performed best for the Congruent Matching Cells (CMC) scores, assuming binomial and beta-binomial models for KM and KNM score distributions respectively. Finally it is demonstrated that individual LRs can be combined to interpret the marks on the entire primer as a whole.
Citation
Forensic Science International
Volume
353

Keywords

objective analysis, firearm mark comparison, computer aided system, interpretation, likelihood ratio, 3D topography

Citation

Baiker-Sørensen, M. , Alberink, I. , Granell, L. , van der Ham, L. , J.A.T. Mattijssen, E. , Smith, E. , Soons, J. , Vergeer, P. and Zheng, X. (2023), Automated interpretation of firearm mark comparison results, Forensic Science International, [online], https://doi.org/10.1016/j.forsciint.2023.111858, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935196 (Accessed March 5, 2024)
Created December 13, 2023, Updated February 9, 2024