NCJ Number
235611
Date Published
August 2011
Length
58 pages
Annotation
This study produced known error rates involved in determining two class characteristics of knives based on the analysis of toolmarks on bone and cartilage created by a knife.
Abstract
The two class characteristics at issue were blade serration (serrated, partially serrated, and non-serrated) and the side of the edge bevel of the blade (left, right, or even). Although the partially serrated blades were sometimes difficult to distinguish from the serrated blades, the partially serrated blades did produce distinct signature patterns that were recognized by the experienced observers. When considering serrated and partially serrated blades as one group, the overall correct classification of blade serration for the study was 96 percent, and observer agreement was strong. Edge bevel was assessed with a reasonable degree of accuracy under optimal conditions (over 83 percent), but not when bone was the substrate (less than 50 percent); observer agreement was moderate, suggesting additional research is needed in order to accurately determine edge bevel. On average, direct compared with indirect (via casts) comparison and the technological level of the microscope did not influence the results. The study made experimental cuts in an ideal medium (casting wax), pig cartilage, and deer bone. Three observers with varying degrees of experience examined the cuts through direct observation of the materials and indirect observation (casts of the material) using two different microscopes (one with enhanced depth of field), resulting in a total of 504 observations. 12 figures, 36 references, and appended images of knives used in the study and a data collection sheet