The distance relationship between an assailant and a discrete bloodstain

Abstract

Discrete bloodstains with a diameter less than 1 mm are often located on objects and people near violent bloodshed events. Historically, forensic specialists have been asked to examine these stains to determine if a person of interest is merely a witness to a crime or the perpetrator. A typical defence in criminal matters is that the accused was in the vicinity of the attack but not the assailant due to some nominated distance from the alleged victim. There is very little published data that assists in the use of such bloodstains to corroborate or refute supplied versions of events. Consequently, legal challenges to exclude further interpretation and opinion by qualified experts can be successful. As the development of usable DNA profiles from very small blood depositions continues to improve, the fundamental question of bloodstain size against distance to the originating blood source remains a critical yet contentious issue. This study employed a custom-designed pneumatic impact apparatus to create submillimetre bloodstains with human blood. The apparatus was developed using experimentally validated force data captured from 36 volunteers wielding improvised household weapons commonly found in real forensic casework. More than 1,000 discrete bloodstains were created and analysed on a non-porous target. Data from these stains were analysed to establish an upper-bound reference linking bloodstain size to maximum horizontal flight distance. The results demonstrated an absolute maxima of drop travel irrespective of significant increases in applied force. Notably, a 1 mm diameter bloodstain was found nearly 2.7 metres from the impact event source, far beyond what kinematic calculations would predict, suggesting that a potential suspect located at that distance could not reasonably be the assailant. Additionally, the study documented interesting artefacts formed during the production and dispersal of impact bloodstains. The primary outcome of this research identified a single logarithmic equation to calculate the maximum horizontal flight distance of drops creating a bloodstain between 0.21 and 1.01 mm in diameter. This equation serves as a critical reference for field calculations and case reporting. The result is an invaluable crime scene and laboratory guide for the criminal investigator, bloodstain pattern analyst, crime scene reconstructionist, and forensic biologist.

Date of Thesis submission	2024
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Val Spikmans (Supervisor), Chris Lennard (Supervisor), Michael Raymond (Supervisor) & Robert Ebeyan (Supervisor)