PhD Dissertations: Diane Cockle, 2013

Human Decomposition and the Factors that Affect it: A Retrospective Study of Death Scenes in Canada

Little is known about human decomposition and the variables which affect it in Canada.  This study involves the retrospective analysis of 358 police death investigations from across Canada. Cases with reliable data were selected using the Canadian ViCLAS (Violent Crime Linkage Analysis System) database. A total of 36 environmental, immediate context, intrinsic and geographic variables were examined for each case.  A classification system was designed based on biological processes of decomposition and a method developed to assign a relative value to each case (Relative Level of Decomposition Value). There are four components to the study. The first component determined the quantitative and qualitative differences in the progression of baseline decomposition for outdoor surface, buried, indoor and water scenes. The frequency of alternate states of decomposition such as mummification, adipocere formation or moulding was determined for each scene type. The second component determined which variables affected the progression of decomposition by scene type.  The PMI (in days) was found to have more predictive value compared to the ADD score. Seven variables were found to contribute to 83% of the variability in the decomposition score outside on the surface.  Within the three other scene types, 2 or 3 variables contributed to less than 54% of the variability in the decomposition score. Independent variables such as alcohol consumption, cold exposure, age, and blood loss were found to have an impact on decomposition; whereas sex, clothing, sun exposure, shrouds, build and burial depth did not.  Insects and scavengers had a limited involvement in all cases regardless of season. The third component of the study found that there were geographical differences in baseline and alternate states of decomposition across Canada.  The last component of the study tested existing formulas for PMI estimations using Canadian cases, with negative results. The variability within baseline decomposition, between scene types and geographical locations precludes the estimations of accurate or forensically practical PMI estimations in Canada. The understanding of decomposition could be used to determine the original context of found remains and predict the extent and type of decomposition given a set of known variables, for search and recovery strategies.

 Keywords:         Forensic taphonomy; human decomposition; PMI estimation; outdoor decomposition; indoor decomposition; variables affecting decomposition.