Interaction of bullets with intermediate targets: Material transfer and damage

In complex shooting incidents, it is not always clear which bullet hit or eventually killed the victim and who fired it. The examination of traces of foreign material embedded in or adhered to bullets provides critical information in the trajectory reconstruction of spent bullets. Such a reconstruction can have considerable legal implications because it can prove that it was not someone's intention to kill. However, the microtraces that remain on spent bullets are often ignored. Microtraces on bullets, around bullet-holes and on ricochet marks were investigated using SEM/EDX for two different types of bullets: a relatively hard, full metal jacket (FMJ) bullet and a relatively soft, lead round-nose (LRN) bullet. A total of 179 bullets were fired into intermediate targets, sheets of 5 different materials (MDF, greenboard, gypsum fibreboard, glass and steel), at approximate incident angles of 90°, 10° and 5°. Of the 144 bullets fired at incident angles of 90°, 130 bullets perforated one of the materials, and 14 bullets perforated two of the materials. The 35 bullets fired at incident angles of 10° and 5° ricocheted off the intermediate targets, producing ricochet marks. In the majority of cases, traces from the target materials were found on the bullet, both after perforation and ricochet. The only exceptions were (1) the perforation of 9-mm sheets of MDF by FMJ bullets and (2) ricochet off glass when the glass did not break. Steel targets transfer small, but still detectable traces of iron to the bullet. The order in which targets are hit was reflected in the traces found on the bullets, i.e., materials from a secondary target were deposited on top of deposits from the primary target. This result implies that it is possible to determine the order of impact from the stratification of the material analysed. Traces from the bullets were found around all the bullet holes. Wipe-off from lead bullets is sometimes visible by the naked eye. Ricocheting bullets produce remarkable traces on glass. The combination of sliding and flattening action leaves a trace of the bullet's surface material in the form of tiny droplets and other evidence of liquid formation. In general, softer LRN bullets are more susceptible to the transfer of material than harder FMJ bullets. For perforation, trace materials are preferentially deposited in a ring-shaped area around the (flattened or unflattened) nose of the bullet.