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| Bloodstain Analysis |
| 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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| 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. |
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| 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. |
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| 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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Revealing Intentions |
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| Blood that leaves the weapon can also
indicate the viciousness behind the attack, as powerfully projected
sprays of blood would suggest that the attack was frantic and unwavering,
with the intention of killing in mind. |
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Spaced Patterns
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| The absence of bloodstains is just
as revealing as bloodstains being present. A space where no blood
is present suggests that there may have been an object laying where
the source of blood was projected and the surface to which the blood
was projected onto. The object that may have been removed by the attacker
will carry the same blood spatter marks as the rest of the area. |
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