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| A lot of blood is lost
during a violent assault and it is these bloodstains
that can reveal a killer. By studying their position,
shape and size, investigators can identify where the
attacker stood during the assault, their height, how
many times the weapon was used, and if the attacker
was left/right-handed. Blood is not easily removed and
therefore makes an excellent tool for reconstructing
the scene. |
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Choose one of the follwing headings
for more information:
--> Finding
the stains
--> Blood
patterns
--> The
origin of the stain
--> Revealing
intentions
--> Spaced
patterns
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| Copyright
Thinkquest Team 00206 |
| Finding
The Stains |
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| To be able to use bloodstains
at the scene of a crime to reconstruct an attack, investigators
first have to find all of the stains. Investigators
commonly use a high- intensity light beam, which when
filtered, produces a violet light useful in locating
bloodstains. If this method does not reveal blood or
if the crime scene has been cleaned, other reagents
that make blood identifiable are used. Luminol and fluorescein
are the most commonly used reagents and can reveal blood
that has been watered down to a ratio of 12 000:1 i.e
12000 parts water to one part blood. Luminol reveals
drops of blood when sprayed in a dark room. The luminol,
on contact with bloodstains, turns fluorescent, making
it visible to investigators. Fluorescein is very sensitive
and only glows if it is lit up with a UV light source.
Both of these reagents react when they come in contact
with iron that is found in haemoglobin
in the blood. |
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| *The
origin and force of impact for blood droplets can be
regenerated with a computer program. Photo courtesy
of Westchester
County NY Forensic Laboratory. |
| Copyright
Thinkquest Team 00206 |
| Blood
Patterns |
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| Patterns in the bloodstains
found at a crime scene reconstructs the actions that
caused the blood to spill and spread. When a droplet
of blood hits a surface, the shape of the mark when
it lands reveals the direction in which the drop was
traveling and the amount of force it was projected with.
Blood that falls for a short distance creates big round
droplets on the floor. Blood that is projected with
a large amount of force breaks into smaller droplets.
When blood hits an angled surface, the droplets run
downwards which creates a tail that points in the opposite
direction to the initial drop. |
| Copyright
Thinkquest Team 00206 |
| The
Origin Of The Stain |
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| Blood
that has been found on the wall, floor and ceiling
can be traced back to where the attacker and victim
were situated at the time. Originally, investigators
analysed each mark and reconstructed its path
using string. With present day technology being
at a high standard, investigators now use computer
programs that take gravity
and the position of the blood into account and
are able to chart an accurate flight path for
the blood droplet.
Definite blood spatter marks
often reveal even more information, particularly
if the blood has been thrown from the tip of
a weapon. Identifying whether the bloodstains
curve to the left or the right reveals which
hand the attacker used to hold the weapon and
the width of the trail of blood can identify
what type of weapon was used in the attack.
Knives leave a narrow trail of blood whereas
baseball bats leave a wider trail of blood.
*Computer
generated images show above, a droplet of blood
from a small height and below, a droplet dropped
from a large height. |
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