Angle of Impact Determination from Bullet Holes

• NCJ Number: 242789
• Journal: Journal of Forensic Identification Volume: 63 Issue: 3 Dated: May/June 2013 Pages: 233-246
• Author(s): Kenton S. Wong; John Jacobson
• Date Published: June 2013
• Length: 14 pages
• Publication Format: Article
• Publication Type: Report (Study/Research)
• Language: English
• Country: United States of America

Annotation

This study determined whether Balthazard's method of determining the angle of impact for a blood droplet can also be used to determine the angle of impact of a bullet that has perforated a solid flat surface.

Abstract

Using tests with wood pressboard, sheetrock, and vehicle sheet metal, this study concludes that the angle of impact from bullet holes that are commonly observed at crime scenes can be approximated using the same trigonometric relationship between the major and minor axis of the observed bullet hole, as concluded by Balthazard for determining the angle of impact for a blood droplet. As a general rule, however, the accuracy of determination of the impact angle for bloodstains is within 5 degrees to 7 degrees; whereas, the current study found that the bullet holes examined tended to produce "much more variable results." Depending on the target media, the production of the bullet hole caused by the bullet's impact may result in tearing and destruction of the target media. Therefore, the original cross-sectional spherical shape of the bullet may become deformed as the bullet distorts upon impact into the target. Using the half-length method with the sheetrock, both examiners reported calculated angles of impact of 90 degrees for the known impact angle of 80 degrees. Conversely, with the wood pressboard, both examiners reported average calculated angles of impact of approximately 80 degrees for the known impact angle of 90 degrees. Such increased error rates in more orthogonal bullet holes requires that examiners carefully consider making conclusions about the direction from which the bullet struck the material when bullet holes indicate angles greater than 60 degrees, because the test bullet holes produced between 70 degrees to 90 degrees were virtually indistinguishable from one another without the context of the known impact angle. 4 tables and 9 references