An assessment of the reliability of cut surface characteristics to distinguish between hand-powered reciprocating saw blades in cases of experimental dismemberment.

Abstract

Criminal dismemberment is most commonly committed with a variety of hand-powered saws. These saws leave characteristic marks upon the bone that can assist in the identification of the weapon utilized. The current study provides frequencies of presentation of ten cut surface characteristics and examines intra- and interindividual variation between three hand-powered reciprocating saws. Pig radii were used as a proxy for human remains. 42 cut surfaces were created with three hand-powered reciprocating saws by the same researcher. Cut surface characteristics were assessed macroscopically, microscopically and with Scanning Electron Microscope (SEM), as well as photographed with Reflectance Transformation Imaging (RTI). Cut surface polish is the only characteristic that demonstrates consistently significant difference between saws. Five characteristics demonstrate some variation between blades: entrance shaving, breakaway spurs, breakaway notches, pull-out striae, and tooth hop. Four characteristics demonstrate no difference between blades: cut surface striation shape, cut surface striation regularity, harmonics, and exit chipping. Tooth hop is the most reliable characteristic for differentiating between blades in this study, while pull-out striae demonstrates high intra-individual variability and a low frequency of presentation making it unreliable for differentiating between saw blades. Cut surface striations, exit chipping, and breakaway spurs occurred with the highest frequencies and were reliable for determining direction of blade progress and blade stroke, but were not reliable for differentiating between saw blades. Harmonics were absent. Further research is necessary to create large databases of known saw mark examples with known intra- and interindividual variability rates and error rates.