Image Processing Based Approach to Determine the Angle of Incidence for Bullet Holes, in Aid of Shooting Incident Reconstruction

Abstract

Identification of a shooter’s location in a shooting incident is a piece of critical information which investigators need to understand for scene reconstruction. Bullet holes and their characteristics play a significant role in tracking bullet paths to their originated locations. Few methods are currently employed to estimate the angle of incidence of fired bullets by means of bullet holes. But each method has its own limitations. The accuracy level of the estimated trajectories depends on many factors. Considering the commonly reported incidents, out of many bullet types and associated target surfaces, the AK family rifles and Zinc coated 1 mm sheet metal are selected for this study. The study analyzed the special deformation features and metal surface debris spread around the outer perimeter of the bullet impact marks, targeting the determination of incident angle. It also demonstrated two inversely proportional mathematical relationships considering the area of the impact mark and the length of the lead-in crease to the incident angle of the fired AK bullet. And it revealed the possibility of using the bullet impact area to predict the approximated incident angles from 10o to 90o and the usability of lead-in crease length to predict the approximated incident angles below 40o, referring to the AK bullets impact marks identified on Zinc coated 1 mm sheet metal in actual crime scenes.