NCJ Number
138365
Journal
Journal of the Forensic Science Society Volume: 32 Issue: 2 Dated: (April/June 1992) Pages: 169-175
Date Published
1992
Length
7 pages
Annotation
The application of Bayes' Theorem to the interpretation of fiber transfer evidence requires estimating the number of foreign fiber types or groups on the recipient garment in question.
Abstract
The Bayesian approach produces an end value, the likelihood ratio, that considers the probability of a suspect committing a crime. A disadvantage of this approach, however, in the absence of information specific to a case, is the need to use values from research work on fibers and their transfer dynamics. To find case-specific values, a study was conducted of undergarments. Fiber tapings were prepared from the garments using 8-inch lengths of adhesive tape. Tapings were rolled, adhesive side down, onto a corresponding length of Clingfilm. The number of different foreign fiber types was estimated. Individual fibers were then removed from tapings and mounted on a microscope slide. The number of foreign fiber types identified on the clothing items after counting with a stereoscope ranged from 15 to 78. Using high-powered microscopy, this range became 19 to 101. Almost 2,800 foreign fibers were removed from the surface of undergarments during the course of the study. They were classified into generic groups and then into one of eight subjective color categories. The generic order of frequency was cotton, acrylic, polyester, viscose, wool, and polyamide. Black and gray cotton fibers represented the most common color type combination. Out of a total of 555 generic/color combinations of synthetic fibers, the number of matching fibers of one type only exceeded 10 in seven instances. It is concluded that a Bayesian approach may be useful in interpreting the evidential value of certain types of trace evidence. 5 references and 1 table