Abstract:
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
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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.
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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.
