Trajectory- the unseen realm in a firing event: a novel and scientific approach in the identification of optimal recovery zones for gunshot residue micro traces.

Gunshot residue (GSR) particles, generated during firearm discharge, disperse in the surrounding environment according to physical laws governing the motion of particles. This study analyzes GSR distribution from 9 × 19 mm ammunition along the trajectory with a fixed target. GSR particle count follows a bell-shaped distribution, influenced by velocity, temperature, and burn rate. Understanding this pattern aids in modeling GSR dispersion based on muzzle-to-target distance, improving forensic analysis of shooting incidents. The kinematic behavior of GSR particles observed in this study facilitated the identification of the region exhibiting the highest deposition. The peak particle deposition was detected along the projectile trajectory, specifically at 100-130 cm from the muzzle end, in the direction of fire. This facilitated the identification of the distance at which the probability of obtaining maximum GSR particles is possible. This aids forensic investigations, providing insights into the trajectory, and identifying the potential region of maximum GSR deposition. A significant influence of distance on the number of GSR particle deposition was observed in the study. The study highlights the necessity of GSR collection along the trajectory, where retrieval probability is higher than at the muzzle or target. A methodology using the Trasoscan Laboratory Imaging System (TLIS) for GSR detection and counting is proposed. TLIS demonstrates potential as a primary imaging tool, with analytical data represented as particle frequency in the shooting vicinity. SEM analysis reveals significant deviations in GSR size distribution across muzzle, trajectory, and target, enhancing accuracy by identifying GSR-dense areas for more precise forensic conclusions. The largest GSR particles were recovered from the target distance (470-500 cm), suggesting surface modifications upon impact, which can be instrumental in estimating the shooting distance. The proposed approach could be implemented in current analytical pipelines or caseworks.