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Reliability Assessment of Current Methods in Bloodstain Pattern Analysis

NCJ Number
Date Published
June 2014
93 pages
This study's objective was to produce the first baseline measure of reliability for the principal methods of bloodstain pattern analysis (BPA) by defining the upper limit of BPA classification reliability, with attention to method reliability rather than analyst competence.
This study determined that bloodstain-pattern analysts use contextual information in making pattern classifications, and this information can influence their accuracy. This shows that the boundary between bloodstain-pattern recognition and crime-scene reconstruction is often blurred. This means that at the stage of pattern classification, additional case-specific information, such as medical findings, case circumstances, and even witness testimony influence analysts' interpretations of bloodstain patterns. This problem is compounded by the fact that current bloodstain pattern classification used in BPA is described in terms of pattern formation mechanisms. This makes them components of a crime-reconstruction theory rather than a summary of pattern characteristics. The supplementary study on superimposed patterns showed that, for the current sequencing methods, the chances of incorrectly concluding the order of blood deposition in a spatter/transfer pattern combination is approximately 12 percent where spatter stains are deposited on top of transfer stains and 17 percent for the reverse sequence. Given these findings, the authors advise that practitioners and agencies should take steps to minimize the effects of contextual information in BPA. In this study, well-trained and experienced bloodstain-pattern analysts examined just over 730 patterns in 2 phases, 1 focusing on rigid non-absorbent surfaces frequently present at crime scenes, and the other on fabric surfaces representing surfaces frequently found at crime scenes, and the other on fabric surfaces representing clothing. Six different pattern types were used during the two studies. The extent of available pattern, the nature of the substrate, and the type of contextual information varied in a balanced experiment designed to determine the effect of these variables on pattern classification accuracy. 29 figures, 32 references, and appended supplementary information

Date Published: June 1, 2014