Characterization and classification of organic gunshot residue from neat smokeless powder, cartridge cases, and the hands of known shooters

Abstract

This study encompasses the detection, characterization, and classification of organic gunshot residue (OGSR) through the analysis of three forensically relevant sample types, including neat smokeless powders recovered from live ammunition, extracts from fired cartridge cases, and the hands of known shooters. Liquid chromatography-tandem mass spectrometry is used as an analytical tool for five manufacturer-grade ammunition brands. The relative detection and quantification of Akardite II, ethyl centralite, methyl centralite, diphenylamine, 2-nitrodiphenylamine, and 4-nitrodiphenylamine is used for chemical characterization and to reveal main chemical changes during deflagration. Classification via discriminant analysis methods is effective for neat smokeless powders and spent cartridge cases, reaching correct classification rates as high as 83.7 %. Alternative chemometric techniques, including k-nearest neighbors and support vector machine algorithms, are more appropriate for residues recovered from the shooter's hands that exhibit greater inter-sample variability. The more challenging traces of hand residues yield correct classification rates of up to 62.7 %, partly due to significant changes in the formation of nitro-diphenylamines and Akardite II in some organic gunshot residue. The findings presented in this study demonstrate that analyzing OGSR can offer valuable insights into the discrimination of manufacturer-spent cartridges and, to some extent, hand residues, assisting in forensic investigations and shooting reconstructions when limited evidence is available.