Effects of decomposition on the recoverability of biological fluid evidence

Several factors that influence the rate of human decomposition have been described in the literature, including temperature, access by insects, humidity and rainfall 1 . These environmental factors, as well as purge fluid released during decomposition 2 , can interact with evidence deposited on the clothing of a deceased individual. The present research assessed how these combined factors affect the detection and identification of blood and semen evidence, as well as subsequent DNA analysis. A 35-45 pound (lb) feeder pig (post-mortem interval (PMI) < 3 hours) was placed on a grassy area within the Boston University Outdoor Research Facility for a period of 22 days or 364.3 accumulated degree days (ADD) during late spring, with the temperature averaging 16.5 o C. Aliquots of 30 μl of either human blood or semen were pipetted onto 1 inch by 1 inch sections of a 95% cotton t-shirt. Twenty-two samples of each type were placed on top of and underneath the pig, as well as a similarly weighted bag of sand (control). One bloodstain and one semen stain were collected each day for a period of 22 days from each location, yielding 8 samples per day. Each sample was analyzed within 30 hours of collection. The blood samples beneath the control showed that environmental factors influenced the results of testing. Rain caused dilution and diffusion of the bloodstains and