Effects of decomposition on the recoverability of biological fluid evidence
Bemelmans, Elena A.
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Several factors that influence the rate of human decomposition have been described in the literature, including temperature, access by insects, humidity and rainfall1. These environmental factors, as well as purge fluid released during decomposition2, 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 oC. 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 the color of the stains changed from red-brown to green-yellow. Kastle-Meyer (KM) testing was positive for all samples and ABAcard® HemaTrace® testing was positive for 14 of 22 samples, with the negative results occurring during days 12 - 21. Two stains that were negative at 10 minutes turned positive shortly thereafter, suggesting that a longer development time may be required for compromised samples. The blood samples placed beneath the pig yielded positive KM results on all 22 days and positive HemaTrace® results through day 10. All bloodstains placed on top of the pig and control yielded positive KM and HemaTrace® results. The blood samples from on top of the pig and control yielded full short tandem repeat (STR) profiles for each of the four days of testing (days 1, 8, 13 and 20). The blood samples from beneath the pig and control yielded full profiles on day 1 only. The three subsequent days of testing yielded a maximum of three alleles per sample, with the majority of samples failing to provide any profile at all. Semen samples from beneath the control began to show a decrease in fluorescence using an alternate light source (ALS) by day 3, and some areas of fluorescence occurred in a different location, indicating that the soluble components had diffused outward from the original region of deposition (ORD). Results for acid phosphatase (AP) and ABAcard® p-30 were mostly positive through day 16. By day 17, the ORD no longer fluoresced or yielded positive AP or p-30 results. With the exception of day 10, sperm were identified on all samples. Semen results from beneath the pig showed that even on day 1, the ORD was only weakly fluorescent and by day 4, fluorescent regions began appearing outside of the ORD. These outlying regions of fluorescence yielded positive results with AP Spot and p-30 testing, but showed few or no spermatozoa when examined microscopically. As the days passed, the ORD were no longer fluorescent and AP mapping and p-30 testing yielded negative results; however, spermatozoa could still be identified in almost all of the ORD through day 22. Semen samples collected from on top of the control showed that semen stains retained fluorescence and tested positive for AP, spermatozoa and p-30 through 22 days of testing. Semen samples collected from on top of the pig yielded similar results until day 16, when the fluorescence began to fade and AP testing did not yield traditional color changes associated with a positive result. By day 18, fluorescence was no longer visible with an ALS at 450 nm or 495 nm, however, UV light yielded positive fluorescence when used during days 19-21. Spermatozoa and p-30 were identified on samples saturated with products of decomposition, even when presumptive screening techniques were negative (450-495 nm) or showed an altered appearance (AP). Semen samples from within the ORD yielded full 16 loci profiles from beneath the pig and both on top of and beneath the control on each of the four days of testing. The samples collected from on top of the pig yielded full profiles on days 1, 6 and 14 and partial profiles on day 20. Samples from beneath the pig on days 6 and 14, which had positive presumptive results outside of the ORD, were also amplified, but failed to yield a profile.