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+ µm) 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. © 2013 The Authors. X-Ray Spectrometry published by John Wiley & Sons, Ltd