Semi-automated digital bullet trajectory reconstruction in craniofacial ballistic trauma

Abstract

Introduction Ballistic trauma demands a close collaboration between the forensic pathologist and the ballistic expert to reconstruct bullet trajectories. These reconstructed trajectories are a result of the measurements obtained during autopsy and the relevant ballistic findings on the crime scene. Low velocity ammunition, unfortunately the most applied ammunition in homicides in our regions, tends to change direction when encountering resistance, the so called ‘ricochet-effect’. During autopsy, those aberrant trajectories can be misleading and difficult to reconstruct especially in multiple hits with interfering trajectories. Methods Post-mortem imaging is performed on each ballistic trauma in our forensic department. In extension, as guidance in the reconstruction of (skull) shot trajectories, we developed a software tool combining the defects seen on the 2D CT data with an automated software program based on a semi-rigid model to extract leading features in the reconstruction of the most probable trajectory. To speed up the manual time-consuming search of these hallmarks (entrance wound, free air and bone particles, gunshot residue in and around the trajectory and the final location of the projectile or the exit wound) an automated software program was created using a semi-rigid model and applying an image registration to extract the leading features and reconstruct the bullet trajectory in an automated way. The data to “teach” the automated recognition was obtained under predetermined controlled conditions with several ammunitions under various fire angles using sheep heads. Conclusions Using 3D visualization these results can help the pathologist during the autopsy in determining the trajectory and the ballistic coordinates of the trajectory and can later be shown as documentation in court.