The analysis of gunshot residue (GSR) in forensic science can be used to link suspects to crimes, and link multiple crimes together, as well as providing police with intelligence. In the UK one of the most popular calibres of ammunition for target shooting is .22 Long Rifle (.22 LR). Limited research has been carried out to date on organic residues from this calibre, with most research focusing on inorganic residues or on other calibres more common in the USA and Europe. This research establishes a complete approach for collecting, sampling and analysing propellant and organic gunshot residue, and develops a bespoke, automatic interpretation method to allow fired cartridge cases to be linked back to unfired propellant through a database. The software was developed in Python and is available as Open-Source Software.
Unfired propellant and spent cartridge cases from three brands of .22 LR ammunition (Winchester “Pistol”, Eley “Contact”, and Geco “Rifle”) were analysed using an established method of solid-phase microextraction (SPME), gas chromatography (GC) and mass spectrometry (MS). SPME and GC-MS have previously been shown to be effective for analysis of gunshot residue. It has been possible to distinguish propellant and GSR samples from different brands, and link samples from the same brand together, based on the chromatograms and compounds identified by mass spectrometry.
The chemical compositions of the propellant and GSR from these brands are outlined. Possible further optimisations for the method to improve detection for different calibres of ammunition are also detailed.
View GunShotMatch GitHub (coming soon).
> Read about it on the Staffordshire University Blog
Poster presented at Staffordshire University GradEx 2018. First place in the Forensic Science category.