Microbial Clocks for Estimating the Postmortem Interval of Human Remains at Three Anthropological Research Facilities

As submitted by the proposer: Estimating the postmortem interval (PMI) is a critical step in many crime scene investigations. Current methods such as those that rely on insects or chemical decay products are limited because they may only work for a short duration, are specific to particular geographic regions, are not very accurate, or a combination of these factors. In our previous NIJ award (2011-DN-BX-K533), we demonstrated that microbes provide an accurate clock that starts at death and relies on ecological change in the microbial communities that normally inhabit a body and its surrounding environment (e.g., gravesoil). We showed that microbial communities change systematically after death in mouse, swine, and human model systems. In our proposed research, we will extend these studies in several ways that are beneficial to crime scene investigation with experiments using donated human bodies at forensic anthropology facilities. We will meet NIJ’s Applied Research Goal by improving our understanding of microbial evidence, specifically the accuracy and reliability of microbial clocks across outdoor sites in Tennessee, Texas, and Colorado. We will investigate whether the microbial clock of corpse decomposition ticks at the same rate in different geographic regions and in different seasons. Furthermore, we will test whether microbial community changes can be used to estimate PMI in bodies that have been dead for longer periods. We will accomplish this by examining the microbes that invade bones after an extended decay period, to determine whether the pattern of bone colonization by microbes is predictable and clock-like. Together, these results will allow us to build and test an algorithm to estimate PMI across geographic regions and seasons, thus making it generally useful for crime scene investigators. Finally we fulfill NIJ’s Innovative Areas of Research Opportunities by using the microbiome as a tool for improving medicolegal investigations of death. While this project focuses on PMI estimations, these data are directly applicable as trace evidence for locating clandestine graves and may also provide insight on the relationship between postmortem microbiology and determining cause of death when microbial agents are suspected. This project will bring together a multidisciplinary team of scientists 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, and a video for members of the general public as well as the wider forensic science community. This project contains a research and/or development component, as defined in applicable law. ca/ncf