The secondary transfer of gunshot residue: an experimental investigation carried out with SEM‐EDX analysis

Abstract

Gunshot residue (GSR) is produced when a firearm is discharged and is routinely used in the forensic reconstruction of incidents involving firearms. SEM-EDX with automated detection and analysis software was used to investigate the extent of GSR secondary transfer following the discharge of a firearm. A series of experiments, which mimicked real-world scenarios, was set up to explore these under-researched mechanisms. The findings demonstrate that relatively large amounts of GSR can be transferred to an individual immediately after the discharge of the firearm, through contact with the hands of the shooter or handling of the gun. While varying between runs, over 100 particles were transferred via a handshake in one instance, and it was found that even very large particles (60-100+ mm) were transferred from the shooter to the second individual via a handshake. The findings have implications for forensic investigations, including highlighting the need to sample from individuals who might have been involved in transfers and underscoring the importance of achieving accurate particle counts using the SEM-EDX method. Most importantly, the findings suggest that the presence of GSR (especially in small quantities) may not always indicate that a person discharged a firearm and that the possibility for misidentification of the shooter exists, as does the potential to distinguish shooters from those who have acquired GSR through secondary transfer. Further experiments employing automated SEM-EDX are suggested, which will add to our understanding of GSR transfer evidence and continue to improve the accuracy of interpretations which are presented in court.

An experimental investigation of the indirect transfer and deposition of gunshot residue: Further studies carried out with SEM–EDX analysis

“…The first experiment was designed to extend a transfer scenario simulated in the previous study [8] in order assess the potential for tertiary transfer. The second enabled measurement of the quantity of GSR deposited on a bystander under the same conditions.…”

“…It is not known how these quantities of GSR compare to those that undergo tertiary transfer, or those that are deposited on bystanders. By simulating further transfer and deposition scenarios under the same conditions as the French et al study [8] and by building a more comprehensive picture of GSR transfer and deposition, this present study allows such comparisons to be made. Experimental scenarios were intended to mimic, firstly, a forensic scenario in which a subject who was not present at the scene of a shooting made contact with an individual (perhaps an accomplice) who had previously made contact with a shooter.…”

“…A study by French et al [8] concerning the secondary transfer of GSR reported the occurrence of secondary transfers of GSR to subjects who had made contact with a shooter, and to subjects who had handled a recently discharged handgun. Importantly, these transfers involved significant quantities of GSR and as many as 129 particles were detected on a subject who had shaken hands with a shooter.…”

“…Experimental studies offer a means of improving our understanding of the dynamics of GSR transfer and deposition, and assisting the forensic reconstruction of firearms incidents. This paper develops the French et al [8] study by presenting the results of two experimental scenarios in which tertiary transfers and depositions on a bystander were simulated. The tertiary transfer of different forms of trace evidence has previously been observed (see Taupin [9] for an example regarding fibres and hair).…”

“…This paper contributes to our understanding of GSR transfer by comparing tertiary and secondary transfers in terms of their efficiency and of the sizes of particles involved. The French et al study [8] compared the quantities of GSR deposited on shooters to those recovered from secondary transfer recipients. It is not known how these quantities of GSR compare to those that undergo tertiary transfer, or those that are deposited on bystanders.…”