Radiological detection of gunshot redisue in firearm wounds

Introduction Estimation of the firing range is often critical for reconstructing gunshot fatalities, where the main measurable evidence is the gunshot residue (GSR). After-death events, such as putrefaction, autolysis, incineration or extensive burning of the body, can alter the typical macroscopic and microscopic characteristics of firearm wounds, hampering or at least complicating the reconstruction of gunshot fatalities. Aim of the research project The present study aimed at evaluating and comparing the amount and differential distribution of GSR on fresh, decomposed, and charred gunshot wounds, utilizing a micro-computed tomography (micro-CT) analysis. Materials and methods A total of 110 experimental shootings at different firing distances (5, 15, 23, 30, and 40 cm) were performed on human calves surgically amputated for medical reasons. As controls we used 30 stab wounds, produced with an ice pick on calf sections. Sixty specimens (10 for each tested distance and 10 stab wounds) were immediately formalin-fixed. Forty specimens (10 gunshot wounds from 5, 15, and 30 cm, and 10 stab wounds) were enclosed in a cowshed for 15 days, before formalin-fixation. Forty specimens (10 gunshot wounds from 5, 15, and 30 cm, and 10 stab wounds) were placed inside a wood-burning stove for 4 minutes at a temperature of 400°C. All the samples were analysed by a micro-CT coupled to an imaging analysis software. Results Micro-CT analysis with three-dimensional image reconstruction detected GSR particles in all the investigated entrance wounds. In fresh specimens, GSR was concentrated on the skin surface around the entrance hole, and in the epidermis and dermis layers around the cavity. In decomposed specimens the high-density particles were detected only in the dermis layer. Regarding the charred wounds, the GSR deposits of the firearm lesions inflicted at very close distance (5 cm) were mainly constituted of huge particles with an irregular shape and well-delineated edges; at greater distances, agglomerates of tiny radiopaque particles scattered in the epidermis and dermis layers were evident. No GSR was detected in exit holes and stab wounds. Statistical analysis showed a nonlinear relationship between the amount of GSR deposits and the firing range. Conclusions Our study, which is the first application of micro-CT analysis in the field of forensic ballistics, demonstrates that micro-CT could be an objective and rapid tool for the analysis of gunshot wounds in firearm fatalities. On fresh samples, this method may be of practical use for estimating the firing range given a known percentage of the GSR deposit, while in bodies in advanced decomposition or extremely damaged by fire, it might furnish precious information on the nature and means of productions of an injury, playing an important role for reconstructing the shooting incident. For estimating the sensitivity and specificity of the proposed method, it will be necessary to test the micro-CT, analysing specimens of forensic caseworks and confirming the positive results with a “gold-standard” method.