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Objective Evaluation of Subclass Characteristics on Breech Face Marks
Author(s) -
Riva Fabiano,
Hermsen Rob,
Mattijssen Erwin,
Pieper Pascal,
Champod Christophe
Publication year - 2017
Publication title -
journal of forensic sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.715
H-Index - 96
eISSN - 1556-4029
pISSN - 0022-1198
DOI - 10.1111/1556-4029.13274
Subject(s) - subclass , cartridge , face (sociological concept) , identification (biology) , statistics , mathematics , computer science , point (geometry) , probabilistic logic , combinatorics , artificial intelligence , medicine , pattern recognition (psychology) , engineering , geometry , immunology , biology , social science , botany , sociology , antibody , mechanical engineering
Subclass characteristics can be found on the breech face marks left on spent cartridge cases. Even if they are assumed to be rare and their reported number is small, they can potentially lead to false associations. Subclass characteristics have been studied empirically allowing examiners to recognize them and to understand in which conditions they are produced. Until now, however, their influence on the identification process has not been studied from a probabilistic point of view. In this study, we aim at measuring the effect of these features on the strength of association derived from examinations involving subclass characteristics. The study takes advantage of a 3D automatic comparison system allowing the calculation of likelihood ratios ( LR s). The similarities between cartridge case specimens fired by thirteen S&W .40S&W Sigma pistols are quantified, and their respective LR s are computed. The results show that the influence of subclass characteristics on the LR s is limited, even when these features are prevalent among the potential sources considered in a case. We show that the proportion of firearms sharing subclass characteristics should be larger than 40% of the pool of potential firearms for the effect to be significant.