Temporal analysis of inorganic and organic gunshot residue (GSR): implications for forensic viability.

Abstract

Gunshot residue (GSR) serves as crucial trace evidence in firearm-related investigations, aiding in reconstructing events and establishing shooter involvement. Despite extensive research on GSR, limited information exists regarding the long-term stability, degradation, and preservation of its components particularly under real-world forensic laboratory conditions. This lack of foundational knowledge hinders the reliability of GSR analysis, especially when delays occur between evidence collection and analysis. In India, the absence of standardized storage protocols and the use of varied storage media-such as zip-lock bags, Eppendorf tubes, glass vials, polypropylene boxes, and Falcon tubes raise concerns about the chemical and physical stability of both organic (OGSR) and inorganic (IGSR) GSR components. These diverse storage practices, often based on material availability rather than scientific validation, may impact on the evidentiary integrity of GSR samples during routine casework. Additionally, due to operational challenges such as limited manpower and case backlogs, forensic laboratories frequently experience delays ranging from hours to weeks between the collection and analysis of GSR samples. These time lapses can influence the composition of GSR, yet few systematic studies have evaluated the degradation patterns over extended time intervals. To address this gap, the current study investigates the stability of OGSR and IGSR under realistic storage and analytical delay conditions. The objective was to simulate common forensic laboratory scenarios and assess whether time and storage variables influence GSR composition. GSR samples were stored under uncontrolled ambient conditions, and temperature and humidity were monitored throughout the study (average 28 ± 3 °C; RH 45 ± 3%). Inter-week analyses were conducted on day 1, day 15, day 30, day 45 and day 60 using Raman Spectroscopy for OGSR and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for IGSR. The results demonstrated that both OGSR and IGSR particles remained chemically stable over time, with no significant variation in their spectral or elemental profiles across all time intervals and storage conditions. Minor fluctuations observed in IGSR concentrations were attributed to factors such as non-uniform particle distribution or fragmentation during discharge, which have been previously reported and are not indicative of chemical degradation. These inconsistencies were found to have negligible impact on overall composition and do not compromise evidentiary value. This study highlights the robustness of GSR particles under variable storage conditions and delayed analysis scenarios. The findings underscore the importance of establishing standardized protocols for GSR evidence handling to ensure consistent, reliable forensic outcomes. The insights gained provide a foundational framework for forensic agencies to develop guidelines on the storage, preservation, and analysis of OGSR and IGSR, thereby enhancing the evidentiary value of GSR in criminal investigations.