In this study, time-dependent differences in ribonucleic acid (RNA) decay rates were examined to extend the time frame over which early postmortem interval (PMI) estimates can be made.
The accurate determination of time since death, or postmortem interval (PMI), can be critical in the investigation of suspicious deaths. Knowing when a suspicious death occurred can limit the number of potential suspects to those without a viable alibi for the time of the crime. The forensic techniques currently used to determine PMI - pathology, entomology, and anthropology - are accurate over different time periods following death. A large gap in time exists between the capabilities of forensic entomology and traditional anthropology, leaving a period in which PMI is difficult to estimate. In the current study, comparing the decay rates of a large, labile segment of β-actin RNA and a smaller, more stable, non-overlapping segment of the same RNA from tooth pulp, enabled estimation of PMI values of pigs buried within a shallow grave for up to 84 days. This compares favorably to an estimate of PMI using insect data. Full skeletonization and loss of insect activity was observed by day 28 of the study. In addition to differences in RNA decay rates, morphological changes were observed in the pulp as it aged postmortem. To provide a quantitative measure of progressive color changes, analysis of digital photographs of each tooth's pulp were used to construct a simple colorimetric assay. This assay was then used to cluster ages of pulp samples by color. The two assays, used in combination with one another, can create a more precise estimate of PMI. The potential advantages of this molecular means of estimating PMI include extending the time frame for such estimates, being applicable to samples collected worldwide (no specialized knowledge of local insect fauna is required), and being relatively fast and inexpensive. (publisher abstract modified)
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