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| Time
Since Death |
| 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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Select one of the following topics for more information:
--> Body
temperature
--> Hardening
--> Truth
lies in the eyes
--> Skin
colour
--> Blood
pooling
--> Digestive
system
--> Forensic
entomology
--> The
body farm
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| Copyright
2004-2005 Thinkquest Team 00206 |
| Body
Temperature |
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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. |
| Copyright
2004-2005 Thinkquest Team 00206 |
| Hardening |
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| 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. |
| Copyright
2004-2005 Thinkquest Team 00206 |
| Truth
Lies In The Eyes |
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| 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.
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| Copyright
2004-2005 Thinkquest Team 00206 |
| Skin
Colour |
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| 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.
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| Copyright
2004-2005 Thinkquest Team 00206 |
| Blood
Pooling |
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| 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. |
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| The
Digestive System |
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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 ennormal, 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 abennormalities 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.
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| Forensic
Entomology |
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| 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.
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Time
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Physical Appearance of Body
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Insects Present at that Stage
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| 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. |
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| The
Body Farm |
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| 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. |
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