Experimental study of postmortem change under field conditions: effects of freezing, thawing, and mechanical injury.

Understanding the processes of postmortem change in biologic systems is important to the forensic sciences. Previous experimental studies of postmortem change in animals under field conditions made use of animal carcasses that had been incidentally exposed to the effects of freezing and thawing or mechanical damage, or both, and were limited to gross observations. The current study was designed to document intrinsic processes of postmortem change, and the effects of freezing-thawing and mechanical injury, under controlled conditions in the field, using histologic and microbiologic techniques, as well as gross observation. Insect and microbiologic succession sequences, and patterns of decomposition and disarticulation, were observable over time. Previously frozen-thawed animals showed predominantly decay (aerobic decomposition) in the field, while freshly killed animals showed predominantly putrefaction (anaerobic decomposition). Previously frozen animals showed the same sequence, but accelerated rates, of disarticulation. Mechanically injured tissues showed accelerated rates of decomposition. These findings have implications for the interpretation of results of previous studies, as well as the interpretation of human and animal remains subjected to freezing and thawing.