At the Lab: Estimating Time of Death
Sometimes there are witnesses who can state with certainty when a person died; other times there may be evidence such as a closed circuit video recording or a broken watch that can provide the same information. In the absence of direct evidence such as this, it is up to the coroner to estimate the time of death (T.O.D.). To do this, the coroner will consider the findings of experts such as identification officers, forensic pathologists, and sometimes even forensic entomologists.
At the unique open-air crime lab known as the Body Farm, decomposing corpses help detectives solve murders. Watch the 3:37 minute National Geographic "Welcome to the Body Farm" video. Warning: graphic images of decomposing human bodies. (Viewing is optional).
At the unique open-air crime lab known as the Body Farm, decomposing corpses help detectives solve murders. Watch the 3:37 minute National Geographic "Welcome to the Body Farm" video. Warning: graphic images of decomposing human bodies. (Viewing is optional).
National Geographic. 2011. Welcome to the Body Farm.
Warning: graphic images of decomposing human bodies. (Viewing is optional). |
A gunshot wound to the head—was it suicide or homicide? Foray into a real-world forensics case as detectives scramble to solve the mystery. Watch the 3:55 minute National Geographic “Real Life CSI : Crime Autopsy” video. Warning: graphic images of an actual autopsy. (Viewing is optional).
National Geographic. 2007. Real Life CSI: Crime Autopsy.
Warning: graphic images of an actual autopsy. (Viewing is optional). |
5 Methods for Estimating Time of Death
Body Temperature
- When a person is alive, cells are hard at work performing important functions for the body.
- The work of these cells is what ultimately creates our body heat.
- This heat is then moved throughout the body by the blood.
- One of the first things that happens after death is the body temperature drops until it equals that of the surrounding environment.
- This happens because the cells stop working and the blood stops moving.
- Theoretically, the body will cool at a constant rate per hour, and this can be used to estimate T.O.D.
- Factors that affect the rate at which the body cools: the room temperature, outside temperature, the amount of clothing the victim is wearing, and the percentage of body fat.
- So Body Temp will only provide a very rough estimate of T.O.D. It is important to supplement this estimate with other information.
Rigor Mortis
- Rigor is the gradual stiffening of the body after death due to the build up of waste materials (lactic acid) in the muscles.
- Ordinarily waste is removed from our cells by blood, but when the heart stops beating this process also stops.
- Rigor starts 3 to 8 hours after death, and lasts up to 36 hours.
- After that, chemicals in the body begin to break down and the body loses its stiffness.
- The exact length of time before a body passes through rigor depends on many factors: level of exertion prior to death, percentage of body fat, illness, environmental conditions.
Liver Mortis
- After death, blood starts to pool in the areas of the body closest to the ground.
- This causes dark blue or purplish patterns to appear on the skin in those areas.
- This condition is called livor mortis, or post-mortem lividity.
- Livor mortis begins immediately after death and starts to become visible 1 - 3 hours later.
- Within 6 - 8 hours it is fully visible.
- Livor mortis will not develop in areas where there is pressure against the skin, such as contact with the ground or another object, as the capillaries are compressed.
- Not only can livor mortis assist in establishing T.O.D., it can also give clues as to whether the body has been moved.
- For instance, if a man is found dead in his bed, you would expect to see livor mortis on the parts of his body closest to the mattress.
- However, if the livor mortis pattern appears only in his lower body, this would suggest he was standing at the time of his death and was laid down afterwards.
Stomach Contents
- Another clue for estimating T.O.D. is the last meal eaten by the victim.
- Digestion of food stops immediately upon death.
- This means that the amount of digestion that has occurred will sometimes allow the forensic pathologist to estimate when the last meal was eaten.
- It could also give an indication of cause of death since any drugs may not be fully digested.
- May also give clues to a person's whereabouts. Popcorn eaten in the middle of the day may suggest that the person was either at a matinee movie or at a fairground.
- Contents with RoD will sometimes help investigators find the location and time of the victim's the last meal.
- May lead them to witnesses and/or suspects.
Insects
- Study the insects that appear on or near a body after death.
- Different species arrive at different times, depending on the body's stage of decomposition.
- Knowing this can help a forensic entomologist estimate when a person died.
- Insects arrive on a body almost immediately after death.
- The first to arrive are blowflies.
- Knowing which species of blowflies are on the body and which developmental stage they are at can help an experts pinpoint with reasonable accuracy when the person died.
- As temperature increases, insects develop faster
- As it cools, they develop more slowly.
- These facts change time of death estimates.
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Important Terminology
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