In a criminal trial that involves a death, it often is critical to know when the person died. But law enforcement and medical examiner communities need more accurate and standardized methods, with known error rates, to estimate time since death.
To help get us closer to those standards, National Institute of Justice-supported researchers from the University of Tennessee, Knoxville, designed and demonstrated a new method for estimating time since death (postmortem interval) that builds on the commonly used Megyesi et al. method for measuring human decomposition. Using the Megyesi et al. method, forensic examiners divide observations into three portions — head and neck, trunk, and limbs — and assign scores to each section based on the presence or absence of set decomposition criteria. Those scores then generate a total body score — a number that correlates to observed human decomposition stages. The new method calculates a decedent’s total body score by summing decomposition scores from 16 regions of the body instead of three.
The researchers, led by Giovanna M. Vidoli, said their method has the potential to significantly impact medicolegal death investigations by providing law enforcement agencies with scientifically-derived data that could meet Daubert standards for admissibility of evidence in federal court.
In addition, the team applied geographic information system technology to the decomposition scores to map different rates of decomposition for the 16 observed body regions and to visualize overall trends in human decomposition for the Knoxville, Tennessee climate.
Project Design and Methods
Vidoli and her colleagues aimed to improve postmortem interval estimates by simplifying and standardizing the total body scoring process. Instead of the Megyesi et al. approach of combining several traits into each of the three body region scores — for example, a single score accounting for the drying and discoloration of skin on the arms and legs — the researchers developed a scoring method for 16 regions of the body using a standardized list of traits recorded as either present or absent.[3] The new method also accounts for tissue loss due to scavenging activity.
To test their new method’s ability to accurately estimate postmortem interval, the researchers conducted eight seasonal trials with 51 human donors with known times since death. For each trial, three to 10 human donors were simultaneously left to decompose undisturbed at the Anthropology Research Facility at the University of Tennessee.
Every day, a primary observer and seven secondary observers scored each body region of each human donor directly into a tablet computer. Temperature data were also collected daily.
For each day of the trial, the 16 body region and scavenging activity scores were summed for a total body score and combined with temperature data to calculate an estimated postmortem interval. The researchers compared this value with the known postmortem interval (the first day of the trial) and with the postmortem interval calculated using the Megyesi et al. method. They also looked at the rate of decomposition for each of the 16 body regions separately.
Data Analysis
The predictive power of the researchers’ new model showed that it more accurately estimated postmortem interval than the Megyesi et al. method, as shown by a coefficient of determination value of 0.9271 versus 0.8456, respectively. (The closer a coefficient of determination is to 1.0, the better the model is at predicting future outcomes.) They also noted that there was no significant difference between the primary observer and the seven secondary observers’ scores, indicating no observer bias.
The researchers used geographic information system technology to visualize how decomposition progressed differently over time for each of the 16 body regions. They found that the abdomen, genitals, upper arms, and upper legs decomposed more quickly than other regions of the body.
Implications for Criminal Justice
According to Vidoli and her team, their new method has the potential to “directly impact the medicolegal community by more precisely estimating the postmortem interval.” The researchers attribute the lack of observer bias to their use of plain language in the protocols and standardized data collection, thus making the new method more accessible to all practitioners regardless of experience or education.
To further meet the needs of the medicolegal community, the researchers said more studies in different geographic regions and climates are necessary.
Republished courtesy of NIJ. Photo: Researchers working at the Forensic Anthropology Center at The University of Tennessee, Knoxville. Credit: UT Knoxville.