Erasing the Evidence: The Impact of Fire on the Metric and Morphological Characteristics of Cut Marks
Ashley Hutchinson · California State University ScholarWorks (system-wide DSpace) · 2011
ABSTRACT ERASING THE EVIDENCE: THE IMPACT OF FIRE ON THE METRIC AND MORPHOLOGICAL CHARACTERISTICS OF CUT MARKS by Ashley Hutchinson Master of Arts in Anthropology California State University, Chico Fall 2010 The aim of this study is to provide a preliminary framework for understanding how fire affects the survivorship of cut marks on bone. This study analyzed the survivorship of cut marks, striations, and metric changes of kerf size associated with burning. There was an expectation that most cut marks would survive the fire, although changes were expected such as that the previous damage to bone would lead to extensive fracturing in the areas of the preexisting trauma. An understanding of how fire affects cut marks on bone is important when attempting to determine a particular class of tool based on cut mark features. Because the use of burning to hinder identification and destroy evidence are common challenges faced by forensic scientists, understanding that fire may change trauma characteristics is important when attempting to draw conclusions about a suspect weapon. With kerf xi width being a criterion for assessing tool class, forensic investigators need to understand that if bone is burned, this method may not be able to be used to eliminate suspect weapons. For the purpose of this study cut marks were created on pig (Sus scrofa) femora using a cleaver, hand saw, scalpel, and steak knife. From these cut marks, casts were made and then analyzed using a digital microscope. The total number of cut marks present on each bone was noted, and widths were taken at three intervals along the length of each cut mark. Once casted, the pig femora were burned in a controlled building fire for approximately 45 minutes with the temperature ranging from 277.3??C- 1,096??C. The surviving cut marks were casted again. The results from this study were quite variable between the different tools. With only 47.2 percent of the cut marks surviving the fire, the bone with cut marks created by the cleaver demonstrated extensive fracturing. Survivorship was much higher for the cut marks for the scalpel (68.8%), steak knife (88.6%), and hand saw (72.5%). Paired t-tests were conducted to determine the significance of width changes among the different tools. The results were drawn from the second width measurement, taken at the approximate center of each kerf. Paired t-tests yielded results that indicated that only the cleaver had non-significant changes in width. Both the scalpel and the saw showed a significant decrease in width. Percentages were also determined for the survivorship of striations from the cleaver, saw, and steak knife. The saw had the highest survivorship (81%), followed by the steak knife (43.8%) and the cleaver (0%). The scalpel did not demonstrate striation characteristics. xii These results suggest that burning does have a significant effect on cut marks on bone. Bone with perimortem trauma is prone to extensive fracturing due to fire exposure, which may lead to a loss of observable traumatized bone. In regards to width change, as the overall bone shrinks and warps, there is a decrease in cut mark width. While there does not seem to be a consistent pattern between serrated and nonserrated tools, it is clearly shown that fire has an impact on the metric characteristics of cut marks. These results indicate that after fire exposure, width can no longer be utilized as a line of evidence for assessing tool class.