Beyond the shot: Exploring secondary transfer of gunshot residue on common surfaces and the impact of hand cleaning methods

Abstract

Understanding the presence, transfer dynamics and depletion of gunshot residues (GSR) on various surfaces is crucial for preserving evidence, reconstructing shooting incidents, and linking suspects to crime scenes. This study aims to explore the transfer and loss of GSR on commonly encountered surfaces such as ceramic, glass, metal, paper, and plastic, as well as the influence of different common hand cleaning methods on secondary transfer. Using scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX) and automated detection software, we quantified highly indicative three-component characteristic particles (lead, barium, and antimony) on cups made from ceramic, glass, metal, paper, and plastic. Furthermore, we evaluated the amount of secondary transferred particles on these surfaces following various post-discharge hand cleaning methods: washing with water and soap, washing with only water, wiping with wet wipes, or using paper towels.

The results demonstrate that counts of secondarily transferred GSR particles vary significantly among surfaces. Specifically, the transferred GSR count was highest on paper, followed by plastic, ceramic, metal, and glass respectively. Post-discharge hand cleaning methods, including washing with water and soap, washing with only water, cleaning with wet wipes, or with paper towel, resulted in substantial loss of GSR count on transferred surfaces. Among these methods, washing with water and soap showed the highest depletion. The empirical evidence provided by our results underscores the importance of considering surface properties, post-shooting activities, and the methods of sample collection and analysis when interpreting transferred GSR analysis. Despite challenges, these insights enhance our ability to link suspects to shooting crimes through careful consideration of the entire context.