Human Decomposition: Effect of Indoor Versus Outdoor Decomposition on the Microbiome of Human Cadavers and Implications for Future Forensic Research

Estimating the postmortem interval (PMI) is a critical step in many crime scene investigations. Current methods such as those that rely on taphonomy or insects are limited because they may only work for short duration and therefor may not be very accurate. Bacteria are credited as a major driving force for the process of decomposition. Modern techniques investigate the bacterial community structure of carrion and cadavers using high-throughput sequencing. While these studies provide valuable insight into the microbiome associated with decomposition, they all use data gathered from either controlled laboratory studies, outdoor decomposition, or single samples from real-world forensics cases. Human remains decomposing indoors may experience an altered trajectory of decomposition likely due to alteration of several abiotic factors; however, controlled studies investigating decomposition indoors are greatly lacking. If shelter can alter the tempo and mode of decomposition by changing microbial succession patterns, approximations of the postmortem interval based off models developed for outdoor studies will lead to erroneous estimations of the time since death. Longitudinal studies on cadavers decomposing under natural conditions in a sheltered environment would close a large gap in scientific knowledge. In our proposed research, we will investigate the influence of shelter on microbial evidence, specifically the accuracy and reliability of microbial succession of human cadavers across two treatments over two seasons (indoor and outdoor; spring and winter). These results will allow us to build an algorithm to estimate PMI, fulfill NIJ's Innovative Areas of Research Opportunities by using the microbiome as a tool for improving medicoleagal investigations of death, and train students for a future-focused workforce. While this project focuses on PMI estimations, these data are directly applicable as trace evidence and may provide insight into the relationship between postmortem microbiology and determining cause of death when microbial agents are suspected. This project will bring together a team of scientists with success in microbial collection and analysis and the exploitation of advances in DNA sequencing technology that allow characterization of microbial communities at one millionth of what the project would have cost a decade ago. We will disseminate the results through presentations, workshops, open-access publications for members of the public as well as the wider forensic science community. Note: This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14). CA/NCF