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When a body is discovered (as opposed to a set of bones), the
first procedure is to identify it via such things as its gender,
age, dental features, blood factors, scars, fingerprints and
personal effects. Whether or not that's successful, the time
of death must be established as soon as possible after discovery.
It is one of the central factors in any murder case and can
eliminate suspects, break alibis, or place victims clearly with a
suspect. The sooner after death this is established, the more
accurate it is.
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| A medical thermometer
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At the site of the crime the coroner or medical examiner makes an
informed guess at the approximate time when the individual expired,
because it will then be subject to photographs, transportation, and
other delays, and over that period of time there will be changes in
the corpse. At the very least, the ME should take a
temperature reading with a rectal thermometer and examine body
coloration and eye fluids. |
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Time of death estimation is based on a variety of changes
following death, because they generally proceed in a predictable
order. None are wholly reliable, since all are affected by
diverse factors, but taken together, they can provide a good
estimate. These include:
- Food digestion
As in the Lynne Harper case, an examination of her stomach
contents, along with the knowledge of exactly when she had eaten
her last meal, placed the time of death approximately two hours
after eating. Although this was based on an assumption
that the stomach digests food and empties into the intestines at
a predictable rate, in fact many things can influence this
process. The type of food, the body's metabolizing rate,
the presence of drugs or medication, and the person's emotional
condition prior to death may all have some effect on how fast
food is processed. Even exercise right before death can
slow it down, and the amount consumed. A light meal may
remain about two hours, a heavy meal from four to six hours.
Examination of the small intestine is also done to trace the
path of the food.
- Body temperature (algor mortis)
After death, the body is no longer taking in oxygen for
maintaining its normal temperature of 98.6 degrees Fahrenheit,
so it begins to cool at the rate of approximately one to one and
one-half degrees per hour until it takes on the temperature of
the surrounding medium (air, water, dirt). A
rule-of-thumb formula that some forensic personnel follow is:
98.6 – rectal temperature, divided by 1.5 = approximate number
of hours since death
However, several factors can affect this. If the weather
is cold, the temperature may drop more quickly than on a warm
day, but an obese person tends to cool less quickly than someone
with little body fat. Heavy layers of clothing can act as
insulation, and some drugs raise the body temperature prior to
death.
- Discoloration (livor mortis)
Also known as postmortem lividity or hypostasis, this refers to
the dark purple color of the body that is found closest to the
ground where it's lying. It appears about one to two hours
after death and becomes fixed within eight to ten hours.
Lividity is caused by blood darkening and settling into the
lowest parts because the heart has stopped pumping it through
the body. The white and red cells no longer mix and the
red cells settle to the bottom. Only the parts of the body in
contact with something that causes pressure will prevent the
blood from settling there. A person found lying on her back will
exhibit lividity on her back. If lividity instead appears
on the front or one side, that means that the corpse has been
moved since death. Skin that is discolored but blanches
when touched indicates that lividity is not yet permanent, and
that helps to indicate that the death was more than two hours
earlier but probably not as long as ten.
Some deaths will have a different appearance. Carbon
monoxide poisoning, for example, keeps the blood a bright red
color, and bodies that have lost a lot of blood will not
discolor.
- Rigor mortis
Right after death, the body goes limp, but within fifteen
minutes to fifteen hours, the muscles begin to stiffen from
accumulating waste products. The average amount of time
for this to begin is two to three hours after death. It
first shows in the face, lower jaw and neck, and over the next
twelve to eighteen hours spreads throughout the body. The
rigid muscles contraction can last up to thirty-six hours.
Then the stiffness disappears, beginning again in the head and
neck area. It may take as long as ten hours from start to
finish for the corpse to be entirely flexible again.
Factors that affect the onset and release include the presence
of heat, which speeds it up, and differences in musculature.
It is also the case that not all obese people develop this
stiffness, and not all muscle rigidity is actually from rigor.
"Cadaveric spasm," which is an immediate stiffening of
the hands and arms, is the effect of extreme agitation or
tension just before death. A suicide gripping a revolver,
for example, is not necessarily in a state of rigor. It
has happened that valuable trace evidence, such as a suspect's
hair, was found in a victim's tightly-clenched hand.
- Decay/decomposition
Immediately upon death, microorganisms that live in the body go
to work to dissolve the internal organs. They produce gas,
which bloats the body before it eventually escapes. The
face darkens and liquids escape the nose and mouth. The
tongue swells and the abdomen begins to turn a greenish-yellow
color. Eventually the skin blisters and fills with fluid
or gas. If the weather is warm and humid, putrefaction may
set in within a day, but when left in a very cold area or
storage space, may be retarded for several months.
If left in a place where flies can get to it, the body becomes
host to maggots, and the larval stages can also help to
determine time of death—although shifting climatic conditions
can affect the developmental progress by several hours.
(An elderly woman's death in England had initially been
determined to have taken place on a certain day, but a study of
how the heating controls in her home had extended the stages of
larval development revised the date to an earlier
time—coinciding with the presence of the suspect in her area.
He had an alibi for the initial estimate, but not for the final
one.) Different species of insects can help determine if a
body has been moved from one location to another, and some lay
eggs only during daylight hours.
Bodies found in a moist area may develop a waxy substance from
the decomposition of body fat, known as adipocere. It
makes the body float in water and can preserve the internal
organs. (In Scotland, the bodies of two children found in
a river nearly two years after their death were covered in
adipocere; as a result the contents of their stomachs were still
fresh enough to determine their last meal, which lead right to
the killer---their father.)
Very dry air may produce mummification, in which the body
tissues dry and harden.
- Ocular
If the eyes remain open after death, a thin film forms on the
surface. The potassium content from the breakdown of red
blood cells enters the eyes and within two to three hours, they
look cloudy. Eyes that are closed develop the same
conditions, but it takes much longer; the cloudiness may not
occur for an entire day. This process is not affected by
the ambient temperature and some pathologists think that it's a
more reliable measure of time of death than the other five.
- Personal factors
Aside from indicators in the corpse, other factors during the
investigation may also play a part in estimating time of death.
If someone was last seen or heard from at a certain time, then
obviously that person was not dead. If he or she had an
appointment and failed to show up, that also helps. Lynne
Harper was seen on a road at a certain area just after 7:00
p.m., and a boy coming along that same road shortly thereafter
saw no one.
No matter how many factors one might identify for complicating
the time of death estimation, investigators must always be alert to
those that have not yet been documented, such as in the following
case.
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