Quantitative image analysis of gunshot soot patterns on white fabrics for muzzle-to-target distance determination

When a firearm is discharged at close range, a dark soot deposit may be visible on the victim's clothing surrounding the bullet entry site. The presence and distribution of this residue carry significant forensic value, particularly for estimating the muzzle-to-target distance. Traditionally, distance determination is performed by visually comparing the crime-scene sample with test-fired samples produced using the suspected firearm or by referencing an established database. This study introduces a novel image-analysis-based method to extract and quantify black pixel counts from soot patterns on white fabrics, using five firearm types commonly encountered in crime investigations. Soot patterns from five common firearms (Type 56 rifle, Browning HP pistol, SLR rifle, M16 rifle, Uzi SMG) fired at 1-8 inches onto white Tetron cotton were digitised with a camera, processed via custom software, and analyzed for pixel counts and coefficients of variation (CV). The findings demonstrate that the dark pixel counts derived from digitised soot-pattern images can provide a reasonable quantitative reference for soot deposition on white cloth at varying shooting distances, showing consistent coefficients of variation across samples. Additional field tests using different weapons of the same make and model as those employed in the quantitative analysis indicate that soot patterns on white fabrics may be distinctive to specific firearm-distance combinations, suggesting the potential for individualisation. These results underscore the promise of this method as a robust and reliable tool for forensic applications, pending further technical refinements to address existing practical limitations.