Pattern injuries from blows with the muzzle end of a handgun

Injury pattern and the biomechanical assessment of skull fracture risk in blows with a rubber mallet

Acts of violence often result in blunt force trauma. On behalf of the court, forensic experts not only have to assess injuries in terms of morphology or severity, but they also have to give statements regarding the risk of potential fatal injuries. We describe a case of domestic violence where a man hit the head of his wife using a rubber mallet. His wife sustained extensive and multiple parietal scalp lacerations and avulsions with exposure of the cranial bone. A CCT revealed neither skull fractures nor intracranial injuries. Biomechanical measurements were performed using a bowling ball and an animal head representing head surrogates. In comparison to steel hammer impacts we hypothesized longer contact durations and lower maximum contact forces in blows with a rubber mallet. However, contact durations in the magnitude of 3ms do not confirm our hypothesis. The contact forces calculated based on mallet and animal head accelerations were between 2.97kN and 4.68kN. These force values are rather below the parietal fracture thresholds, explaining the absence of parietal skull fractures in the case presented. Moreover, the relatively low Young's modulus comes along with a deformation of the rubber mallet and a decrease in contact pressure. In summary, contact times could be reliably estimated, while contact forces remained largely uncertain.

Bullet wipe on the uppermost textile layer of gunshot entrance sites: may it be absent due to pre-existing blood staining?

Most gunshot entrance sites on human victims are localized in clothed body regions. Except for the use of lead-free ammunition, a positive color reaction of the sodium rhodizonate test indicates a primary target hit by the bullet. Any lead residue pattern in the area around the entrance hole allows approximate conclusions as to the firing distance in close and intermediate range shots, whereas the presence of a bullet wipe denotes an entrance site. A criminal case gave rise to an experimental study to clarify whether a blood-soaked garment being shot at as a primary target may lack a bullet wipe around the entrance hole. Distant-range shots were fired with a semi-automatic pistol (Heckler & Koch, Mod. USP Compact, cal. 9-mm Luger) using cartridges with jacketed round-nose bullets and a Sinoxid primer containing lead styphnate. In fabrics saturated with fluid blood, a wide area around the bullet entrance was densely covered with rhodizonate-positive microparticles simulating gunshot residues (GSR) from a close-range shot. In shots to fabrics oversaturated with blood, a typical bullet wipe was lacking, whereas lead-containing particles were spotted in the periphery. The results are discussed with respect to the aberrant appearance of bullet entrance sites in blood-soaked fabrics.

Wound morphology in contact shots from blank cartridge handguns: a study on composite models

It is a well-known fact that blank cartridge guns can cause penetrating and even fatal injuries when discharged in contact or at very close ranges. In these cases, the gas jet perforates the skin leaving an entrance wound similar to that from a conventional gun. In order to investigate the wound morphology in contact shots from blank firearms, test shots were fired at composite models of pig skin and gelatin blocks using three different calibre 9-mm blank cartridge handguns (two pistols and one revolver) and two types of ammunition. It turned out that the penetrating gas jet produced roundish skin defects resembling bullet entrance holes. Small skin particles from the perforation site were dispersed in the underlying simulant where radiating cracks containing greyish gunshot residues indicated the original expansion of the inrushing combustion gases. Apart from the size of the permanent entrance hole in the skin and the final position of the displaced tissue particles, the penetration depth of the gas jet was determined. Under the specified conditions of the test shots, the zone of mechanical destruction within the simulant was 2.2 to 6.1 cm in length, which illustrates the injuring potential of contact shots inflicted with blank cartridge handguns.