Abstract
The accurate estimation of postmortem interval (PMI) is crucial in the investigation of homicide cases. Unlike carcasses on land, various biological and abiotic factors affect the decomposition of carcasses in water. In addition, the insect evidence (e.g., blow flies) that is commonly used to estimate the PMI are unavailable before the carcasses float on water. Therefore, it is difficult to estimate the PMI of a carcass in water. This study aimed to explore an effective way of estimating the PMI of a carcass in water. Carrion insects, brain tissue RNA, bacterial biofilm on the skin surface, and algae in water with PMI were studied using 45 rat carcasses in a small river. The results showed that carrion insects might not be suitable for the estimation of PMI of a carcass in water since they do not have a regular succession pattern as a carcass on land, and the flies only colonized six of the carcasses. The target genes (β-actin, GAPDH, and 18S) in the brain tissue were associated with the PMI in a time-dependent manner within 1 week after death. A polynomial regression analysis was used to assess the relationship between the gene expression profiles and PMI. The correlation coefficient R2 of each regression equation was ≥ 0.924. A third-generation sequencing analysis showed that the bacteria on the skin surface of the carcass and the algae in the water samples around the carcass had a regular succession pattern, where Cryptomonas and Placoneis incased and decreased, respectively, within first 9 days. The results of this study provide a promising way to use the brain tissue RNA, bacterial biofilm, and algae to estimate the PMI of a carcass in water.
Highlights
Unlike carcasses on land, various biological and abiotic factors, such as temperature, water depth, and aquatic organisms, affect the decomposition of carcasses in water (Sorg and Haglund, 1996)
This study aimed to evaluate the potential value of insects, RNA, bacteria, and algae for postmortem submersion interval estimation using a rat model
The carcasses were found still floating during the last sampling on day 18, with approximately 1/3 of the soft tissues missing, and no carcasses entered the stage of sunken remains in this study
Summary
Various biological and abiotic factors, such as temperature, water depth, and aquatic organisms, affect the decomposition of carcasses in water (Sorg and Haglund, 1996). Aquatic insects usually cannot be used as the indicators to estimate the postmortem interval (PMI) of submerged carcasses. The body of water blocks most terrestrial sarcosaprophagous insects, making it difficult for them to reach the carcass (Merritt and Wallace, 2009). Even if a few insects can colonize the carcass during the floating stage, the insect evidence can only provide the PMI after the carcass. PMI-Estimated by Four Indicators has started floating, which is usually different from the real PMI owing to the uncertainty of the time at which it is submerged (Amendt et al, 2007; Merritt and Wallace, 2009). All of the factors mentioned make it difficult to estimate the PMI of a carcass in water, and methods of reliably estimating PMI are urgently needed for submerged carcasses
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