Rapid Search and Quantitative Analysis of Gunshot Residue Particles in the SEM

Abstract

Automated scanning electron microscopy coupled with image analysis and X-ray micro analysis was used to characterize a variety of gunshot residue (GSR) samples. More than 500 rounds of commercially available ammunition and six different types of hand guns were used in the study of 17 GSR and 19 reference specimens. The individual particle X-ray composition was determined for 12 different elements. Elemental composition of GSR particles was highly variable but consistent with compounds mixed into or associated with a barium oxide matrix. When present in a specimen, GSR could be adequately characterized with automated procedures in less than an hour by restricting analyses to features larger than 2 µm. In “clean” samples, a higher resolution particle search was required to avoid reporting false negatives. Careful control of the back scattered electron signal strength threshold, by reference to a standard, was needed to ensure both time-efficient and accurate analyses. Samples collected from non-shooting subjects, active in a physical environment which contained firearms discharge residue were seen to be easily contaminated by sub-micron GSR particles.

Distribution of gunshot residues – The influence of weapon type

“…Consequently, any contaminated surface, especially the weapon itself, can render a ''positive'' result merely from touching [2]. Accordingly a person does not even have to be present in a given location during the shooting event to get a chance of carrying GSR particles.…”

“…with sodium-rhodizonate or with ICP-MS, XRF, NAA or AAS, the EDX-analysis in a SEM is commonly used (e.g. [1][2][3]). Most of these analytical methods try to confirm the presence of specific heavy metal remains from the primer of a cartridge (i.e., particulate metal condensates).…”

Recent developments in methods of chemical analysis in investigations of firearm-related events

“…Miayauchi et al [23] demonstrated the contribution of trace elements from smokeless powder to primer residues. Lebiedzik and Johnson [24] reported that indicators of the type of weapon and of the ammunition used in firing can be obtained from the distribution of GSR shapes and compositions.…”

The survival of metallic residues from gunshot wounds in cremated bone: a SEM–EDX study

“…However, most of the studies which have attempted to apply these techniques to gunshot wounds deal with cadavers in a relatively good state of preservation, whereas very little literature exists on gunshot wounds on charred material: the analysis of GSR on gunshot entrance wounds in charred samples has never been performed [10][11][12][13][14]. What remains of these residues in charred material?…”