Interpretation of cast-off patterns in bloodstain pattern analysis. Traditional approaches and their pitfalls

When reconstructing the course of crime-relevant events, analyzing patterns of cast-off blood is an important concept. In the current literature, a controversy exists whether the perpendicular line underneath a pattern of circular bloodstains defines the positions of the perpetrator and victim. The aim of this study was to test whether cast-off patterns are located directly above the position of the perpetrator or the victim. Cast-off patterns with defined positions of a test subject (perpetrator) and blood source (victim) were experimentally generated and analyzed using standard measurement equipment. Cast-off bloodstain patterns were present at a linear position above the perpetrator as well as above the victim. Circular bloodstains were not found directly at a perpendicular position above the perpetrator but at a distance of approximately 35 cm in front. Their position was therefore more above that of the victim. The most common interpretive approach found in the literature states the perpetrator's position to be perpendicularly underneath circular cast-off bloodstain patterns. The results of this study indicate that this is not always applicable. The corresponding prerequisite conditions and pitfalls are discussed.