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Assessing Error in PMI Prediction Using a Forensic Entomological Computer Model

NCJ Number
Date Published
October 2004
37 pages

This study examined the thermal behavior of forensically significant maggots, the effect of internal maggot mass heat generation on maggot development time, and the sources and magnitude of error that affects a phenological computer model for predicting the likely postmortem interval (PMI) of human remains found long after the person's death.


Field studies were conducted in north Florida and northwest Indiana using 88 domestic pigs placed in a wooded setting and allowed to become colonized by blowflies and other carrion-feeding flies and insects, while being protected from larger scavengers. Adult flies found around the corpses were collected and identified; and samples from maggot masses were characterized by species and life stage, as well as measured for dimensions and temperature. Some pigs were monitored with a linear probe that continuously measured the internal temperature of the pig and masses in 12 locations along the probe. Using an expanded computer model, researchers conducted simulations that used weather data from the Florida test plots; PMI predictions were compared to actual results in the field trials. For the few useable field trials, the time-of-death estimates of the computer model were accurate to within an error rate of 1-2 percent; however, the majority of the field trials were not useable because there was no phenology data for the most common fly found. The trials can be run when phenology is obtained for that species. The most sensitive parameter in the model is the growth rate of the maggots, followed closely by air temperature, which becomes less important as the mass grows larger and has better internal temperature regulation. Larger sample sizes yielded greater precision in the model. 2 tables, 13 figures, 9 photos, and 81 references

Date Published: October 1, 2004