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When a gun is fired, nano to micron sized particles are deposited on the shooter and anyone in close proximity to the vapour cloud that is formed by the combustion of the bullet's primer. The particles that make up this gunshot residue (GSR) is very diagnostic of a gun having been fired. Oxford Instruments provides hardware and software that meets the international standard ASTM E1588, and which automates the process of finding the particles on an SEM stub, by measuring their composition and imaging, and measuring their morphology.
Typically, the forensic examiner wants to establish how many particles have been detected on a suspect that are characteristic of GSR. In order for this to be completed effectively, they require a high degree of accuracy and reliability with a reliable, repeatable method and, in many cases, the ability to work quickly as throughput is often an issue. Whilst ICP-MS is a sensitive approach which was commonly used, however this is a destructive technique where the original particles are lost in the process. This also removes any morphological evidence of the particle as it is dissolved in the preparation process. The sphericity of the particle improves the quality and validity of the evidence gathered. We therefore recommend that the task is best addressed with a combination of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).
Ammunition is constantly being developed, mainly to address the composition of the primers to reduce toxic components which could impact on regular shooters. This however creates an extra complication for examiners as the GSR particles that are detected by these lower-toxicity ammunitions are harder to detect than the classical lead-bearing ones. This is where Automated SEM and EDS can facilitate the examiner by considering the range of particles that are found. The specific combination of particles with different compositions can be indicative of specific ammunitions, meaning that it is possible to get an indication of the brand of ammunition that was used.
Gunshot residue (GSR) is produced from the condensation of the vapour cloud which is generated from the primer and propellant when a bullet is fired from a gun. The condensing vapour from the primer will form particles which are typically spherical and range from potentially less than 0.5 μm up to significantly larger sizes...
The combination of X-Max Extreme, a windowless, large solid angle detector, and AZtecGSR enables the automated detection of particles containing light elements such as boron at very short acquisition times. Here we show how that enables the identification of particles from new, heavy metal free ammunition types in the analysis of gunshot residue.
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