Report on High Velocity Bloodstain Patterns

The NIJ, through the National Criminal Justice Reference Service, has made available a technical report about high velocity bloodstain patterns.

The report, Quantitative Analysis of High Velocity Bloodstain Patterns was written by Professor William Ristenpart, Fred Tulleners, Sonya Siu, Jennifer Saifi, and Faye Springer, all of University of California Davis.

Excerpt from the Authors' Abstract:
The goal of this study is to establish statistically significant classifications of blood spatter patterns resulting from the interactions between a weapon, suspect and victim. Specifically, a “medium velocity” spatter pattern is usually attributed to blunt force injury, while a “high velocity” pattern is typically attributed to a gunshot wound. The differentiation between these classifications, however, has been qualitative and controversial. There are neither supporting statistical data nor are there objective criteria as to what constitutes “consistency” or the associated error rate.
We obtained two key findings. First, we demonstrate that quantitative metrics involving the spatially-dependent size distribution of droplets within a spatter pattern could serve as an objective means of differentiating gunshot and blunt instrument spatter patterns. Second, our double blind investigation revealed that human assessments yielded low error rates for gunshot spatter patterns (0.2%), but very high error rates for blunt instrument spatter patterns (37%).
Our findings strongly suggest that (i) great caution should be exercised when identifying a pattern as resulting from a gunshot or blunt instrument impact in the absence of secondary indicia, and (ii) that further effort should be put toward development and refinement of quantitative image analysis procedures based on droplet spatial distributions.
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