Forensic
science provides a number of solutions to solving the
mystery question of when a person died. Generally, the
longer it has been since the death, the less accurate
the estimation given by forensic pathologists.
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Police
arriving at the scene of crime should be capable
of estimating how long a person has been dead
for, by judging from the body temperature and
stiffness of the corpse. However, a more accurate
evaluation of the time since death must be made
by a forensic pathologist in the forensic laboratory.
The pathologists/coroners record the temperature
of the body, the temperature at the scene of crime,
the weight of the victim and all other appropriate
variables, which are then applied to a formula
designed to predict the time since death. The
core body temperature drops at an estimated rate
of 0.8K each hour from the time of death, but
is ever-changing dependant the surrounding temperature,
humidity levels, air movement and fat levels in
the body. Thus, the less time that has surpassed
since the death, the less variables which will
affect the prediction.
*Temperature
is an effective measure of the time since death
in cases where the victim died within a matter
of days. Photo courtesy of www.freeimages.co.uk.
Stiffening of the corpse
occurs between just 30 minutes and 3 hours after death.
The process is called rigor
mortis and occurs as the muscles in the body
begin to stiffen from a lack of blood and oxygen. Rigor
mortis first becomes apparent in the eyelids and jaws
of the victim and spreads throughout the whole body
in approximately 6 to 12 hours, before receding again
after another 6 to 12 hours. Occasionally, stiffening
of the body may not even occur if the surrounding temperatures
are very low, while the process occurs a lot quicker
in muscles that were quite active before death. Like
body temperature, the evidence provided by the level
of muscle stiffening becomes of little use after a long
period since death.
The eyes
of a victim can also hold answers to the time of death,
as a thin cloudy film is developed over the eye within
3 hours after death has occurred. The eyeballs become
softer as a result of less fluid pressure behind the
eye and the degree to which this has occurred can be
used as a measure of the time since death. Again, a
less common procedure for deaths that evidently occurred
out of the limit of several days.
*A
computer generated image of the eyes after death. Diluted
pupils and a cloudy film are apparent. Photo thanks
to www.imageafter.com.
The colour
of the corpse will also help determine the time of death
from about 48 hours and onwards. From approximately
48 hours after death, bacteria begins to breed on the
skin, giving the skin an evidently greenish tone. The
tinge starts in the lower stomach area, spreading outwards
and affecting the hands and feet last. Approximately
4-7 days after death, the skin will acquire a marble-like
appearance, as the veins in the body become closer to
the surface, thus becoming more easily visible.
The pooling of the blood
can be a vital clue in determining the time of death
and is known as hypostasis.
This occurs when the blood ceases flowing, settling
in the lowest parts of the body and in turn, causing
the skin to become pink and red in colour. This process
is complete in up to 6 hours after death. The main use
of blood pooling analysis actually lies in helping to
determine the death manner (noting that the location
of the blood pools indicates the upright position of
the body at the time of blood pooling) The process does
however, form a method of predicting the time since
death.
The digestive system
and gut contents of a victim can provide important
clues to the time of death of a victim. Chewed
food will firstly pass through the oesophagus
and then down into the stomach within seconds
of the initial swallowing. After 3 hours, the
food then leaves the stomach and heads toward
the small intestines. 6 hours after eating a
meal, the food will have traveled half way through
the small intestines and begin moving through
the large intestine. Where the victim's small
intestine is empty, it suggests that the victim
ate his or her last meal approximately 8 hours
before death. The digestive process usually
takes a bit more than a day, but it can be affected
by sickness, liquid intake, fear or drug intake.
Pathologists also briefly note
that correct level of food digestion
corresponds to its location in the digestive
system. In the rare case that a clever murderer
wishes to delude investigators by attempting
to bring forward the time of the victim's last
meal (giving them an explanation for where they
were at the victim's time of death), he/she
may manually feed processed food (resembling
that of chewed food) into the victim's stomach.
If this is so, the food collected in the stomach
will be much less digested than normal, since
the periodic motion of the stomach stops after
death. The food may indeed appear slightly broken
down, due to the presence of the stomach acids,
but any abnormalities are otherwise detectable.
In older people or in those affected by the
effects mentioned earlier (sickness, fear, drug/liquid
intake), the efficiency of food digestion alters
and it is left to pathologists to determine
if the extent of the undigested food is great
enough to suggest the mentioned scenario.
*
The digestive system includes the eosophagus,
stomach, liver, gall bladder, duodenum, pancreas,
ascending/ transverse/ descending colons, rectum,
anus, appendix, cecum, small intestines and jejunum.
Photo courtesy of Your
Digestive System and How It Works.
Flies
and maggots
also provide an approximate time of death, very useful
for cases where the body has been long dead. Only certain
insects will feed and lay eggs on a dead corpse and
forensic entomologists study these insects, their larvae
cycles and thereafter can determine whether a body has
been dead for just one day or up to 3 or 4 weeks.
*Larvae
development is a good indicator for deaths which concern
a matter of months. Photo courtesy of Valeri
Craigle and the Spencer
S. Eccles Health Sciences Library.
Time
Physical Appearance of Body
Insects Present at that Stage
0-3
days
0-3
days Proteins and carbohydrates in the deceased
body begin to break down.
Blowflies
e.g. Bluebottle flies, Syrphidae flies
4-7
days
Body
is starting to decay and causes the abdomen to
inflate because of the gases inside.
Fly
larvae and beetle e.g. Rove Beetles
8-18
days
8-18
days Decay is well and truly setting in; the abdomen
wall begins to break down.
Ants,
cockroaches, beetles and flies
19-30
days
The
decaying body enters a stage know as 'post-decay';
in wet, humid conditions, the body is sticky and
wet; in hot dry conditions, the body is dried
out.
Beetles
and mites e.g. Springtail beetle, Acari, Nematocera
(present only during the winter months), Brachycera
31
and over days
The
bones, skin and hair that remain no longer give
off a powerful stench and smell just like the
soil surrounding it.
Decay can also determine
how long a person has been dead for and in Tennessee,
a special research area has been set up to study exactly
how and why bodies decay. The research farm, known as
The Body Farm, was established in 1981 by Bill Bass,
a professor of forensic anthropology. By having decaying
bodies readily available to study, Bass and his students
discovered a number of factors contributing to body
decay. Some things they discovered include that flies
and maggots will turn a body in to a skeleton in under
two weeks in warmer weather and the face will always
rot first because maggots prefer wet places. He has
also observed how fast bodies decay when submerged in
water, stored in the boot of a car, or wrapped in plastic
and that when a person's head is burnt, that the skull
reaches boiling point very quickly, causing the skull
to explode. If the person head doesn't explode, it means
that the victim may have been shot in the head, allowing
the steam to escape.
