Trajectory reconstruction by analysis of trace evidence on spent bullets fired through building materials: analysis by microscopy and direct analysis in real time

Trajectory reconstruction of shooting incidents can help investigators determine critical case information regarding the number of shooters involved, their location(s), and intent. The examination of trace amounts of intermediate target materials collected on the surface of spent bullets provides crucial information needed for trajectory reconstruction. Determining the origin of an unknown material adhered to a spent bullet allows for the identification of intermediate targets the bullet either contacted or penetrated during flight. Although significant information can be obtained from examination of these trace materials adhered to spent bullets, this aspect of trajectory reconstruction is often ignored. The ability of different bullet types to collect trace materials from intermediate targets and the ability to associate these trace materials to their origin was examined using microscopy and Direct Analysis in Real Time (DART). Full metal jacket (FMJ), jacketed hollow point (JHP), and lead round nose (LRN) bullets were fired into sheets of five different commonly used building materials (oriented strand board, sanded plywood, white melamine board, synthetic PVC board, and medium density fiberboard) to produce a total of 45 spent bullets to be examined. All spent bullets were examined and photographed using a DSLR camera paired with a stereomicroscope. The spent bullets were then examined using DART/MS to determine if any ion profiles generated from the trace materials could be associated with those of the intermediate target building materials which the bullets were fired through. The collection of trace material from all five types used was highly dependent on the type of bullet. Very minimal amounts of trace materials were observed on the majority of LRN bullets, which failed to produce an identifiable ion signature. The FMJ bullets that were fired through PVC material collected trace material that produced an ion profile, while all other building materials failed to transfer to the FMJ bullets. All JHP bullets collected significant amounts of the five building materials tested inside the hollow point cavity and along the nose of the bullet. In every spent JHP bullet sample, the trace material collected produced a unique ion profile. Additionally, MS data from four of the five building materials tested matched the MS data generated from trace material collected on JHP bullets from the respective target materials