Forensic Ballistics

Forensic ballistics is the application of ballistics for forensic purposes. The basis is formed by wound ballistics. Two main mechanisms of injury are differentiated: the crush-mechanism resulting in the permanent cavity and the stretch-mechanism resulting in the temporary cavity. The missile-tissue interactions such as yawing, deformation, fragmentation, and bone contact are explained here and it is shown why the energy deposit or the missile velocity are not the sole or primary factors in determining the severity of a wound. The special wound ballistics of the head including indirect (‘‘remote’’) injuries in the B. Karger Institute of Legal Medicine, University of Münster, Münster, Germany e-mail: [email protected] M. Tsokos (ed.), Forensic Pathology Reviews, Volume 5, doi: 10.1007/978-1-59745-110-9_9, ! Humana Press, Totowa, NJ 2008 139 brain and skull are discussed. Incapacitation is a necessarily occuring inability to perform complex movements and is therefore based on physiological effects independent of psychological mechanisms such as pain or surprise. Immediate incapacitation can only be caused by direct disruption of brain tissue and thus by penetrating gunshots to the head. Ballistic parameters and intracranial trajectories where sustained capability to act is possible are discussed. Rapid incapacitation is produced by massive blood loss via acute cerebral hypoxemia and subsequent unconsciousness. Targets of rapid incapacitation are the heart, aorta, and the truncus of the pulmonary artery. In cases of considerable ballistic injury to the lungs, liver, kidneys, spleen, large arteries or central veins, the latent period until incapacitation will be in the range of one or several minutes (delayed incapacitation). This potential for physical activity is not always exhausted due to psychological factors. Backspatter is biological material propelled retrogradely out of the entrance wound towards the firearm/the hand of the person shooting. Blood and tissue particles are accelerated by the subcutaneous gas effect, temporary cavitation, and tail splashing. Backspatter therefore is common in closerange gunshots to the head where blood and tissue can travel for several meters. The number of bloodstains can vary greatly and the stains are located in a semicircle of almost 1808 in front of the entrance wound. Characteristic for backspatter are small or tiny droplet or splashing stains with the elongated shapes roughly aiming at the entrance wound. Magnification and appropriate lightning are necessary for investigating backspatter. DNA-analysis of stains can establish a clear link between a person or object and a clearly defined gunshot. Contact of a bullet with an intermediate target can alter the trajectory and stability of the bullet. Contact with fragile materials such as concrete, glass, asphalt, or gypsum-board regularly results in abundant deposits on the bullet, which can be visualized by SEM (scanning electron microscopy) and determined by X-ray microanalysis. Ductile materials such as wood and car body parts only transfer scarce deposits to the bullet which can be indicative of the intermediate target. This important trace evidence is not eliminated by subsequent perforation of tissue. Individualisation of deposits on FMJ bullets after perforation of a human body can be successfully carried out by PCR-typing of STRs and mitochondrial DNA. In cases of gunfights, this makes it possible to determine who was killed or injured by which bullet. The person shooting can be identified by additional comparison of rifling marks. Cellular material is recovered by swabbing the bullet, which should be protected against contamination and loss of material.