Bloodstain pattern analysis: looking at impacting blood from a different angle

Abstract

The prevalence of violent crime is at an all-time high, and this steady increase has consequently increased public pressure on the police and forensic scientists to produce more efficient and accurate methods of crime solving. Bloodstain Pattern Analysis (BPA) has become a Routine field of scientific analysis. Although a fairly new field, its capabilities in high-profile cases are well documented. Unfortunately, the science behind BPA is very subjective and relies heavily on the analyst's opinion, which leads to varying analytical approaches and inconsistent outcomes. This paper explores predetermined equations and applies them to various surfaces that are likely to be encountered in a crime scene. The objective of this study is to generate a general equation directly applicable at crime scenes to determine the position of a bloodstain, and which will be used as a substitute for the already outdated and highly subjective existing method. New equations are developed that better fit the data produced when stain size and angle of impact are examined. The equation formulated for the paper surface is ab = 0.1247 (Re ^0.5 We ^0.25)^0.75 D _o D _o + 32.937 with a correlation coefficient of R ² = 0.84; steel gives an equation of ab = 0.1448 (Re ^0.5 We ^0.25)^0.75 D _o D _o + 19.574 with an R ² = 0.83; while plastic gives the most significant correlation coefficient at R ² = 0.91 with an equation of ab = 0.1405 (Re ^0.5 We ^0.25)^0.75 D _o D _o + 17.771. When all data were collaborated for all surface types, a final equation was created exhibiting an R ² value of 0.85: ab = 0.1367 (Re ^0.5 We ^0.25)^0.75 D _o D _o + 23.427. It was found that spines could not be generalised into a specific equation as they are heavily influenced by the impact surface. Difficulties were also encountered when considering surfaces separately; correlations when considering spines only, produced maximum R ² values of between 0.54–0.70 (steel and plastic) which questions the true applicability of spines as a parameter within BPA analysis.

Keywords:

• bloodstain pattern analysis
• forensic science
• angled impacts
• surface roughness