Death Time Determinations
M.F. & E. Investigative Services LLC provides a modern service for Death Time Determinations, applying internationally recognized protocols to use insect biology to determine a time line. The result is provided as a minimum time since oviposition (the laying of eggs) could have possibly have occurred. Note that this is not the actual time of death (ToD), but, because insects generally arrive soon after death it helps investigations considerably by focusing on the time of death providing a time-frame within which to test alibis and events.
How do we do this? Using experimentally derived duration for insect development, which occurs at a set thermally determined rate for each species, so long as the deceased body and the air temperatures are known, the length of time passed since egg-laying can be derived. This is then noted as a accumulated degree hour value or ADH. Accumulated degree hours are a way to express the thermal energy budget available to insect development and can be thought of as the number of degrees temperature accumulated per hour by the insect development.
- insect specimens must be collected and properly preserved so that species identification can take place
- the body and air temperature must be provided
- if possible, a data logger should be in place at the locus for a minimum of one week from the time the crime was discovered
- data from the nearest meteorological station must be provided for one month prior to and at least a week after the discovery of the crime (i.e. matching the time the data-logger is placed)
- knowledge of any medicines, narcotics, poisons or accelerants used by or on the body of the deceased must be notified as these alter the rate of insect development
- an outline of the circumstances of the crime are essential (e.g. time of day; indoors/outdoors; shaded/not shaded; if indoors, were windows open, was the air conditioning/heating on etc.).
We take the data from the crime scene data-logger and using regression analysis, reconstruct a temperature profile at the locus for the period prior to the crime, then super-impose the known insect development onto that profile. This enables determination of the earliest moment post-mortem that egg-laying could have occurred.
The legal question is always how soon after death do insects (e.g.) blowflies arrive. We call this the pre-oviposition period (PoP) and it is impossible to determine with absolute accuracy. In a timed experiment, however, we have measured blowfly arrival at a corpse as little as fifteen minutes after death. Accordingly, unless there are circumstances to suggest otherwise, the ADH projected onto the temperature profile provides a Death Time Determination that approximates the actual ToD.