Impact height and wall distance in bloodstain pattern analysis--what patterns of round bloodstains can tell us.

Bloodstain pattern analysis is a routine procedure in forensic cases that involve bleeding wounds. It utilizes geometric principles to determine the sequence of actions causing the bloodshed and the area of origin, that is, from where the blood originated. The patterns formed by circular bloodstains from drops of blood that hit adjacent surfaces at a 90-degree angle are thought to provide indications of the height of the impact. In this study, blunt force exerted against a pool of blood, which was used as a surrogate for a bleeding wound, was carried out for five different impact-to-wall distances. The blunt force consisted of a hammer head that was dropped from a height of 1.5 m. High-speed photography of the impact and trajectories of the projected blood droplets was analysed. The patterns containing bloodstains produced by the droplets were analysed by measuring the circular bloodstains within the patterns. All the experiments showed that there were two distinct patterns or clusters of circular bloodstains that occurred at different heights above the impact site. The two patterns were a result of different fractions of blood that were projected in a garland or crown-like form of a "Worthington splash" after impact. The findings suggest that patterns of circular bloodstains cannot be used as direct indicators of impact height, but combined analysis of their clusters may lead to indirect determination of impact-to-wall distance and area of origin.