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Study Assesses the Accuracy and Reproducibility of Bloodstain Pattern Analysis

NCJ Number
Date Published
December 2022

Bloodstain patterns can be pivotal evidence, with the power to exculpate or exonerate defendants in high profile cases. Commonly found at the scene of violent crimes, bloodstains are used by experts to piece together a chronology of events. However, bloodstain pattern analysts have been found to reach contradictory conclusions regarding the same evidence. Although admissible in court for more than 150 years, the validity of bloodstain pattern analysis has recently been questioned. With funding from the National Institute of Justice, researchers sought to assess the validity of bloodstain pattern analysis by measuring the accuracy of conclusions made by actively practicing analysts. In what is now the largest study of its kind, they applied their extensive experience in executing “black box” studies of fingerprint, handwriting, and forensic footwear examination to bloodstain pattern analysis. The researchers reported that the conclusions reached by participants were sometimes erroneous or contradicted other analysts, suggesting potentially serious consequences for casework — especially regarding the possibility of conflicting testimony in court. In the absence of widely accepted criteria for conclusion classifications, one cannot, the researchers argue, expect high rates of reproducibility among analysts. Importantly, disagreements among analysts were often the result of semantics. This lack of agreement on the meaning and usage of bloodstain pattern terminology and classifications underscores the need for improved consensus standards. Experts on the study team also felt that many conclusions expressed an excessive level of certainty given the sparsely provided available data.