Preliminary study of gunshot residues in entry holes at different angles: Feasibility of using LIBS to support trajectory estimation.

Firearm-related scenarios can be highly complex, involving multiple shooters, firearms, types of ammunition, victims, and various impact zones. Obtaining the maximum amount of information to connect each piece of the puzzle is crucial for resolving these cases. Currently, new tools are being developed in the forensic field that facilitate both fieldwork and laboratory analysis, enabling the estimation of trajectories, identification of shooters, and more. Among these techniques, the application of Laser-Induced Breakdown Spectroscopy (LIBS) has gained prominence in ballistic forensic over the past few decades. This study aims to evaluate the information that can be derived from analyzing the spatial distribution of elements composing gunshot residues in entry bullet holes at different angles of incidence using the LIBS technique on various surfaces, such as stainless steel, particleboard, and PVC foam board, using both jacketed and semi-jacketed ammunition. Gunshot residues adhering to the surfaces due to material transfer during projectile transit were collected using adhesive film for subsequent scanning. The results of this preliminary study demonstrate that it is possible to obtain an image of the distribution of the gunshot residue elements analysed (copper and lead) within the entry hole. This would provide additional information to support the estimation of the shot direction. Furthermore, differences in the concentration and distribution of copper and lead in the contact area were observed. Although the obtained density map is dependent on the material of the impact surface, in harder materials such as the stainless steel used in this study, it allows for the differentiation between the two types of ammunition, enabling the correlation of the ammunition with the corresponding entry hole.