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Validation of the BackTrack Suite of Programs for Bloodstain Pattern Analysis

NCJ Number
213441
Journal
Journal of Forensic Identification Volume: 56 Issue: 2 Dated: April 2006 Pages: 242-254
Author(s)
A. L. Carter; Jon Forsythe-Erman; Vince Hawkes; Mike Illes; Pat Laturnus; Gord Lefebvre; Craig Stewart; Brian Yamashita
Date Published
April 2006
Length
13 pages
Annotation
This study used the BackTrack set of computer software programs to determine whether Directional Analysis could determine two of the three Cartesian coordinates for the location of the source of blood drops that moved downward to leave stains.
Abstract
The testing found that the BackTrack programs successfully calculated the approximate X and Y coordinates for the location of the source of the bloodstains examined. The calculation of a three-dimensional location of the source of blood drops that produce a bloodstain impact pattern can be done with three methods: the string method, the mathematical or tangent method, and the use of specially designed computer software. For stains produced from fast upwardly moving blood drops, all three methods will produce reasonably accurate calculations; however, when blood drops move downward to produce stains, the string and tangent methods will not perform well because of the parabolic trajectory of the blood drop from the source to the spot of impact. Directional Analysis via BackTrack uses a bird's-eye view of the flight paths of the blood drops to calculate the position of the blood source in the plane of the floor. The parabolic trajectory of a blood drop lies in a plane perpendicular to the floor. The bird's eye or top view of the flight paths looks down on the edges of these planes and sees them as straight lines that converge approximately at the location of the blood source. The testing was done on five bloodstain patterns created for the experiment. For each stain, a 10 ml pool of blood, located at a known (X,Y,Z) position, was struck with a hammer. The testing of the stains was done by a bloodstain pattern analyst who did not know the locations of the blood source. 3 tables, 4 figures, and 7 references