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Quantifying Variation in Kerf Wall Striations Created by Hacksaws and Reciprocating Saws

Sean Y. Greer


Forensic anthropologists are often tasked with examining tool marks left in bone. These marks regularly take the form of striated kerfs, resulting from a saw-assisted dismemberment. Assessing kerfs is a relatively new area of study, and much remains to be learned about the process of kerf formation, and therefore how kerfs should be interpreted. Here, kerf marks in bone made by saws that use a similar repetitive back-and-forth sawing motion are examined using methods of surface metrology. These methods broadly serve to quantify surface topography, including the amplitude of kerf wall striations. Quantitative analysis of kerf surfaces revealed that hacksaws leave more-variable and higher-magnitude striations in bone than do reciprocating saws. However, the differences between kerf walls made by these types of saws are blurred by significant areas of overlap in their morphological parameters. Understanding the variation in kerf wall striation morphology will lead to better assessments of tool mark features by anthropologists in three ways. First, metric evaluations such as this allow for rigorous statistical comparisons of the variation seen in saw kerfs at multiple levels of observation. In doing so, the high potential for over-interpretation and misclassification based on local morphology in kerfs can be addressed. Second, three-dimensional surface characterizations of kerf walls allow access to characteristics such as striation magnitude that were previously out of reach to the forensic anthropologist. Third, this type of work serves to support currently utilized visual standards for differentiating manual saws from electrically powered saws. By evaluating underlying hypotheses about kerf wall morphology thought to result in overall visual differences, it will be possible to better understand why the characteristics currently used work, as well as times when they can be misleading or misused.

KEYWORDS: forensic anthropology, surface metrology, dismemberment

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