Estimation Of The Postmortem Interval

In the actual process of estimating the postmortem interval from entomological data, each case will be unique. Regardless, the process tends to follow the same general sequence of events:

1. The stage or physical state of decomposition based on physical parameters for the corpse should be determined, and any indications of disturbance or dismemberment of the corpse that may have occurred following death are noted. If the community collected under the corpse does not conform to the observed stage during later analysis, the possibility of movement of the corpse following death must be considered.

2. Specimens collected from the corpse and crime scene must be identified as completely as possible. Immature stages must frequently be reared to the adult stage for final species-level identifications. Representative samples of immatures (species and stages) must be preserved properly to provide a record of what was present on the corpse at the time of examination.

3. For outdoor scenes, appropriate climatic data (temperatures, rainfall, cloud cover, etc.) from weather stations and on-scene observations must be obtained. Aspects of the scene that may serve to influence the effects of these climatic factors on arthropod invasion of the corpse should be considered (cover by vegetation, shading by trees, slope of the ground, burial of the corpse). For indoor scenes, the temperatures (automatic heating, thermostat settings, air conditioner) possible for the time period in question should be noted; positioning of the corpse relative to windows and doors may be significant in terms of both heat and solar radiation.

4. From the autopsy report or one's own observations, the sites of infestations by arthropods should be noted.

5. The postmortem interval is estimated. In the earlier stages of decomposition, this estimate may be based on the developmental cycles of dipteran larvae. In simplest form, the time required to reach the most mature stage of development of the earliest arriving species on the corpse under prevailing conditions would correspond to the minimum postmortem interval. Further consideration must be given to factors that could delay the onset of insect activity (climatic factors, wrapping of the corpse, seasonal variation). When these factors are considered, the final postmortem interval estimate may be greater than the estimated faunal ages. During this comparison, both presence and absence of taxa and developmental stage must be considered. For this reason, it is essential that collections from the corpse and the surrounding area be as complete as possible. In general, the parameters for the postmortem interval estimate will become wider as the time since death increases. During the earlier stages of decomposition, the estimate may be expressed conveniently in terms of hours, whereas later it may be in days, months, or even seasons of the year.

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