NCJ Number
215713
Journal
Law Enforcement Technology Volume: 33 Issue: 8 Dated: August 2006 Pages: 40,46,48
Date Published
August 2006
Length
4 pages
Annotation
This article describes the features and uses of BackTrack, a computer software that enables analysts to locate the source of bloodstain patterns by using the laws of physics to simulate how the bloodstain patterns were produced.
Abstract
A.L. Carter created BackTrack in 1989. Carter taught and worked in experimental particle physics for 30 years and is well-known for his work in translating the application of physics principles into computer programs. He became interested in applying physics principles to bloodstain patterns in 1982 when he was asked to develop a science-based training course for bloodstain pattern analysts. The course focuses on how to include the curvature of the flight paths of blood drops when determining the area of the source for the stain. After an overview of Carter's principles for analyzing blood drops in curved paths, this article outlines the features of BackTrack in terms of its advantages over the manual procedure of using strings to portray the path of blood drops that produce stains. Compared to manual stringing, BackTrack uses procedures based in sound science, saves time by using a computer, produces virtual strings that do not sag and are correctly positioned mathematically, uses the latest digital imaging techniques, and produces numerical values for the horizontal coordinates of the blood source's location. The latter feature provides five measured quantities for each stain: width and length of the stains obtained by a unique ellipse fitting routine and three spatial coordinates of the stain's position (X, Y,Z). When a trained analyst uses BackTrack, the analysis produced is recognized by the courts.