Evaluation of the microbial wet-vacuum system (M-Vac®) for DNA sampling from rough, porous substrates, and its compatibility with fully automated platforms.

DNA retrieval methods traditionally used during forensic evidence recovery including swabbing and tape lifting, can have limited effectiveness when used on porous, rough substrates such as bricks and carpet. This is possibly due to the DNA material being dispersed and unreachable for surface sampling techniques. In this evaluation we investigated the effectiveness of the Microbial Wet-Vacuum System (M-Vac®; M-Vac® Systems, Inc., Sandy, UT), as it has been reported to retrieve greater amounts of DNA material from challenging exhibits. A four-stage evaluation was conducted, starting with seeding carpet and brick substrates with a known donor's saliva in two dilutions and comparing the DNA recovery of tape lifting, swabbing, and the M-Vac®. A victim struggle scenario on carpet was then mimicked to compare trace DNA recovery by each method. Two mock scenarios were also conducted; a shirt was submerged in a creek bed for a period of five days to sample for the wearer's DNA, and a car boot was sampled to assess the possibility of recovering a victim's DNA amongst background DNA from the usual car occupants. Finally, the compatibility of the M-Vac® sampling process was optimised for the fully automated DNA lysis and extraction platforms used in the NSW (Australia) jurisdiction by comparing filter subsampling methods. The results from the study were mixed. For bricks, none of the collection methods were effective in retrieving DNA. On carpet, the M-Vac® retrieved the greatest quantities of DNA from the saliva-seeded samples, however, tape lifts outperformed all methods for 'touch' DNA recovery. The M-Vac® retrieved the greatest amount of DNA from the t-shirt recovered from a creek bed as it was able to retrieve the embedded DNA. The final mock case car boot scenario resulted in greater victim DNA recovery from tape lifts, with the M-Vac® more likely to recover mixtures too weak and/or complex to be interpreted. Finally, operational considerations regarding the compatibility of the M-Vac® system with fully automated DNA lysis and extraction are discussed. Considering the substantial time and cost to deploy the M-Vac®, it is recommended to be utilised in casework only after swabbing and tape lifting methods have failed to yield sufficient DNA material, where the substrate properties would likely benefit from the M-Vac's® niche capabilities for retrieving embedded DNA, and low levels of background DNA may be anticipated.

A casework study: The effect of the porcine digestive process on animal carcasses and human teeth.

What happens if a human body is fed to pigs? Although a popular notion in the entertainment industry, no scientific published literature exists that documents this porcine feeding behaviour, nor, more importantly, what elements of the cadaver may survive such a process. A study conducted in 2020, born out of a casework enquiry, aimed to investigate the following two questions; Would pigs feed on a human body? And, if so, what could be recovered post feeding event? Kangaroo carcasses, porcine carcasses (as human analogues) and 90 human teeth were prepared, and fed, to two domestic pigs, in a variety of feed scenarios. Biological traces including bones, bone fragments, teeth and tooth fragments were recovered both post-digestion from the faeces of the pigs, as well as uneaten from the porcine enclosure. 29% of all human teeth were recovered from the study; 35% of which were recovered post-digestion from the faeces and 65% were recovered uneaten from the porcine enclosure, Of the recovered human teeth, 81% were deemed suitable for identification by a forensic odontologist. From the 447 bones recovered from the enclosure, 94% could be identified to a bone type and species. From all 3338 bone fragments recovered from the faeces of the pigs, none retained any morphological traits that would allow further intelligence to be generated. Overall, it was found that pigs will feed on human analogues and will consume soft tissue, bones, and human teeth. Biological traces in the form of bones, bone fragments, teeth and tooth fragments may be recovered both post-digestion from the faeces, or from the porcine enclosure. The biological traces can be used for identification of an individual via forensic odontology, identification of a species via forensic anthropology and may be suitable for DNA analysis. The outcomes of this study generated new avenues for investigation in the case and may be used to inform future operational resources.