Using tooth pulp as the source material, this study examined whether postmortem interval (PMI) can be reliably determined by comparing two different segments of RNA, one which is relatively stable due to small size or the nature of the RNA, while the other RNA segment degrades more rapidly and predictably over time (typically a larger segment).
This method of determining PMI relies on quantitative polymerase chain reaction (qPCR) to determine the amount of one RNA segment relative to the amount of a second RNA segment. Results from applying this proposed method to the tooth pulp of pig heads that had been buried in a shallow grave showed that an equation can be derived for estimating PMI within a 95-percent confidence interval; however, these equations may need to be seasonal-specific (specific over a given temperature range). A better estimate of PMI can be obtained when data are plotted according to accumulated degree days rather than calendar days. Although the pulp from human heads was tested under the same conditions as the pig heads, limited samples rendered the human data inconclusive. Still, the results from pigs strongly support the feasibility of developing predictive PMI equations for humans, given sufficient samples. Compared to the method of estimating PMI from the timing of the life cycle of identified insects that colonize a corpse, the proposed method of estimating PMI can be used for samples collected anywhere in the world without specialized knowledge of insects. In addition, it is more cost-effective and may allow for estimations of extended PMIs beyond what is possible with forensic entomology. The research methodology is described in detail. 2 tables, 5 figures, 32 references, and a listing of publications and meetings where research results were disseminated