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Application of Forensic Entomology To Estimate of the Postmortem Interval (PMI) in Homicide Investigations by the Rio de Janeiro Police Department in Brazil

NCJ Number
Anil Aggrawal's Internet Journal of Forensic Medicine and Toxicology Volume: 5 Issue: 1 Dated: 2004 Pages: 40-44
Janyra Oliveira-Costa; Catia Antunes de Mello-Patiu
Date Published
5 pages
This article describes the application of forensic dipterology (carrion insect study) to estimate the postmortem interval (time lapse between death and discovery of the body) in three homicide cases investigated by the Rio de Janeiro police (Brazil).
In each of the three cases, the postmortem interval (PMI) was estimated by analyzing the larval development rate for the insects found on the body when it was discovered. Since the time frames for a larval development rate are dependent on environmental conditions, especially temperature and humidity, the PMI estimates calculated for the three homicide cases applied the concept of accumulated degree-days (ADD). This involved obtaining the local meteorological data for the 5 days prior to the day on which each corpse was found. These data were supplied by the meteorological station nearest to the crime scenes. In addition, the ambient temperature was measured at the site where each body was found, including the temperature from the mass of larvae and corpse as well as soil temperature at a 10-20 cm depth. This was done to relate the meteorological data from the nearest weather station to the microclimate of the crime scene. The methods used in this work were based on the adaptation of methodologies for the collection, transportation, and rearing of the diptera specimens described by various authors. The stage of decomposition of the corpse was specified according to the morphological characteristics observed when it was found (fresh, bloated, early decomposition, advanced decomposition, and remains), and the accuracy of the PMI estimate was assessed by referring to statements from witnesses regarding when the deceased was last seen alive. Given that temperature is the most important factor that affects the growth and development rate of insects, ambient temperature was used to determine the development time for earlier stages, maggot-mass temperature for later instars, and soil temperature for pupae. Since hourly temperatures were not available, the data were limited to daily maximum and minimum temperatures used to calculate the daily mean temperature. PMI estimates were based on accumulated degree-day units (ADD). The calculation of ADD was based on a standard technique called the rectangle method. This article describes this method in detail and its application to the three homicide cases. In two cases, the PMI estimates based on the biology of Chrysomya megacephala and Cochliomyia macellaria were close to those determined by other investigative means. In the third case, based on C. megacephala, the PMI estimate differed significantly from the real PMI determined from witnesses because of the restricted and delayed access of sarcophagous insects to the body. 4 tables, 1 figure, and 18 references