Estimating the time of death for the deceased is something else that the pathologist will have to do during the course of his autopsy procedures. In addition to this he or she may be called upon at the scene of a crime whilst carrying out their external examinations to try and judge – or best guess – when the victim died.
At the Scene
It may sound silly but one of the first things to do once a crime scene has been secured and all relevant details documented; is to check for a watch. If the victim does have a watch is it broken? If it is then the watch will more than likely have stopped at the time of the individual’s death, especially if they have had a heavy impact or long fall.
It must be said however that the time the individual took their last breath is not necessarily the time at which they died. This may sound bizarre but taking into consideration the human body can function for a period of time without oxygen – the human brain reportedly surviving several minutes without it – then it is reasonable to assume that the time of death may not always be accurate.
Categorising Time of Death
Time of death is categorised in three ways:
- Physiological time of death: The point at which the deceased’s body – including vital organs – ceased to function.
- Estimated time of death: A best guess based on available information.
- Legal time of death: The time at which the body was discovered or physically pronounced dead by another individual. This is the time that is shown – by law – on a death certificate.
One method of estimating the time of death is to measure body temperature. The normal equation for this is:
- 37.5oC – 1.5 oC
This formula equates to the body temperature (37.5oC), which loses 1.5 oC per hour until the temperature of the body is that of the environment around it; known as the ambient temperature. This ambient temperature – depending on how low it is – may take minutes or hours to be reached and this is a good indicator as to how long a body has been in situ. Additionally it is worth noting that a body’s temperature will drop much more slowly if the body has been exposed to extreme cold; such as being left outdoors, submerged in water or icy conditions.
The most common way of taking the temperature of the deceased is to use a rectal thermometer or to take a temperature reading from the liver, which can achieve a more realistic core body temperature.
Rigor Mortis also acts as a good measuring stick for estimating the time of death. This natural process which occurs in all of us when we die and is the natural contracting and relaxation of the body’s muscles caused by changes in the body’s chemical balances.
Rigor normally occurs in the smaller muscles such as those in the face and neck and will work its way down through the body as the muscles become larger. The process normally begins roughly two hours after death and can last for anything from twenty to thirty hours. It is a common misconception that rigor does not leave the body; it will after these time frames have elapsed.
Rigor is one of the most used ways of estimating death as it occurs in the body during the first thirty-six to forty-eight hours.
Forensic Entomology (the study of insects) is another way in which the time of death can be estimated. By studying the insects found at the crime scene the pathologist is able to establish a more accurate time scale depending on which insects are found on the body and what stages they are at in their life cycle. To find out more read our article on Forensic Entomology.