Reoconstruction of bloodstain impact patterns: error rates
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Authors
Gaziano, John Calvin
Issue Date
2017
Type
Thesis
Language
en
Keywords
Area of origin , Impact pattern , Bloodstain , Error rates
Alternative Title
Abstract
The purpose of the study was to determine the error rates in area of origin analyses among law enforcement personnel and to ascertain whether the reconstructions were within acceptable limits. A total of 68 novices in bloodstain pattern analysis (BPA) from multiple law enforcement agencies in Northern California participated in the study. Subjects used two different methods of measuring photographs of bloodstains with known impact (alpha) angles. The subjects also measured the directional compass (gamma) angles of the same stains. Five real bloodstain impact patterns were created and reconstructed by a BPA expert to introduce the variables of gravity and air resistance. An algebraic computer program was coded to create 20,000 synthetic impact patterns from each measurement method, for a total of 40,000 random patterns. Each of the synthetic patterns randomized the subjects’ alpha and gamma measurement data before merging them with the expert’s data to show the amount of deviation in the reconstructed area of origin from the known origin; the X value was 30 cm from a vertical target surface. The results of the study showed that the mean reconstructed difference from the known origin for both measurement methods was slightly smaller than the volume of a racquetball (5.7 cm) and pool ball (5.7 cm to 6.3 cm). This small deviation in the reconstructed origin from the known origin has investigative value in determining not only the location of a bleeding victim, but also the victim’s posture (standing, kneeling, or lying on the ground) while receiving blows.