Estimation of Post-Mortem Interval Using Decomposition Scales for Hanging Bodies

Abstract

The extent of decomposition of a body can be used, in conjunction with accumulated degree days (ADD), to provide an estimate of the post-mortem interval (PMI). PMI estimations are important in aiding police to narrow down the possible identity of a body, and to include or exclude suspects, and also to establish the order of death for inheritance purposes when two or more potential beneficiaries die at around the same time. Previous studies have shown the decomposition pattern in hanging bodies to be different from that of a body on the ground, but the sample sizes used have been small.
This study presents the results of a series of decomposition studies on hanging bodies in a variety of situations; clothed and unclothed, and fully or partially suspended. The study used domestic pigs (Sus scrofa) which enabled large enough sample sizes for statistical robustness. Pigs lying on the ground were used as controls. The pattern of decomposition in hanging pigs was found to differ sufficiently from that of pigs lying on the ground to require the creation of a novel decomposition scoring scale, which was used successfully to score both clothed and unclothed fully suspended bodies, as well as the upper, suspended, part of partially suspended bodies.
The presence of loose, lightweight clothing, which did not impede insect access, was found to affect both the pattern and rate of decomposition in hanging pigs, with the clothed bodies decomposing faster than the unclothed bodies (p < 0.05, F2, 477 = 1238).
The variations in the start weights of the pigs used for these studies was found to have a statistically significant effect on the rate of decomposition for both the hanging bodies and those on the ground (p < 0.05, F5, 714 = 1962) but the effect was so small as to make no practical difference across the range of start weights encountered. The effect of variation in start weight may be of greater concern, however, in scoring very heavy, obese, bodies and may be exacerbated by the increased fat-to-muscle ratios encountered in such bodies.
Finally a set of ADD prediction tables were produced for the hanging and surface pigs. Further work is needed to establish to what extent these tables can be used for humans and, in light of the growing obesity problems in humans, to investigate the effect of weight and increased fat-to-muscle ratios on the pattern and rate of decomposition.