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Shedding of blood is the dramatic accompaniment
to murder committed by violent means. Blood accounts for about 9 per
cent of a healthy person's body-weight and as many murderers have
discovered to their cost, when it is spilled a little goes a long
way. Once blood is shed in any quantity, and especially when
it starts to clot, it becomes very difficult to deal with.
Murderers' attempts to clean up after their violent handiwork often
fail because of blood-traces which adhere tenaciously to their
clothing or to the murder weapon. Blood found at the scene of the
crime has trapped many killers who thought they removed all
incriminating traces. A sensational demonstration of this was
provided by the French detective Gustave Mace in 1869, when he was
interrogating a murder suspect in the room which he believed had
been the scene of a ghastly crime involving the dismemberment of the
victim. Convinced that a great deal of blood must have been shed,
Mace looked about the room but could see no obvious traces.
Then he noticed a marked hollow in the tiled floor. With the suspect
looking on in astonishment, the detective took a jug of water and
tipped the contents on the floor - the water collected in the hollow
area, and when the tiles were lifted their under-surfaces were found
to be caked with dried blood. This discovery led to a murder
confession by Pierre Voirbo and to a triumph of detection for Mace.
Blood is important forensically, and
can yield a great deal of information to the investigator. The first
task in examining suspicious stains is to determine whether they are
blood, and if so, are they human? Once this is established stains
are examined for age, sex and blood group. The shape and pattern of
liquid blood-splashes can help in reconstructing the murder; bloody
fingerprints and palm-prints tell their own story; dried blood on a
suspect's clothing can be related to the victim, the crime scene and
the murder weapon; blood and tissue forced under the fingernails of
the victim during a violent struggle can be linked to the assailant.
Thus a single blood-trace can provide
a wealth of information, and analytical techniques are improving all
the time. Blood dynamics is important not only for narrowing
suspicion on the guilty but also in showing a suspect's innocence.
As in many other aspects of forensic investigation, bloodstains are
taken into account with a variety of other evidence to build up a
pattern of crime.
The investigation of blood at a crime
scene can be broadly divided into a biological approach (serology) and a physics
approach (blood splatter or bloodstain pattern analysis). This fact
file will concentrate on the dynamics of blood evidence.
Examination and interpretation of
bloodstains on and around the body, and of blood-spots, splashes and
smears at the scene of the crime, are an essential part of a murder
investigation. The position and appearance of blood marks on the
body and its immediate surroundings will help the investigator to
reconstruct the crime.
The theory behind bloodstain pattern
analysis is simple: blood is a fluid and will respond accordingly to
the laws of physics. Though rarely the dominant piece of evidence in
an investigation, bloodstain pattern analysis can be important in
the difficult process of reconstructing a violent crime.
Experts begin by taking note of a few
key variables:
- spot size
- quantity
- shape
- distribution
- location
- angle of impact
- target surface
A great deal can be gleaned from the
shape of blood spots and splashes found on surfaces such as floor,
walls, ceiling, woodwork and furniture. The French criminologist
Alexandre Lacassagne noted the correlation between the shape of
blood sports and the position of the victim. Blood dropping
vertically on to a flat surface form a circular mark with crenated
edges, and denotes that the source was stationary at the time. Drops
of blood falling from a moving object hit a flat surface obliquely
and leave a spot shaped like an exclamation mark. An examination of
the shape of obliquely falling blood splashes yields information
about the direction and speed of impact. Such evidence helps
determine the positions of victim and murderer at the time of an
assault, and may also indicate the manner of violence and type of
weapon used.
A line of blood spots on the ceiling
of a room in which violent murder has been committed is likely to
have been made by the killer wielding an axe or bludgeon in an area
over his head. Smears and trails on the floor may be produced by a
wounded person crawling about or by an assailant dragging the body
of his injured victim. Smudges and smears on furniture and doorsteps
leaving bloody fingerprints or palm prints may result from similar
activities. Blood smears tend to start as drops which become ragged
at one edge, indicating the direction of travel.
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Large spots
- the blood
was travelling at a relatively low velocity. |
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Small spots - the blood
was travelling at a relatively high velocity. (More force
equals smaller splatter) |
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Elongated drops - victim
was moving, their speed relative to the amount the spots are
stretched and how far they are spaced apart. (Also indicates
directionality) |
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Contact
- large stain on a surface
caused by contact with a bloody object. |
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Void
in otherwise uniform
splatter - something blocked the blood spray. |
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Cast-off
- straight,
elongated lines of splatter indicating that blood was thrown
by a moving object in a change of direction. (Can show how
many times a victim was struck) |
Even when the blood stain is not evident it may still leave a
tell tail fingerprint. To detect invisible blood stains, the luminol test is used,
which is a chemical sprayed on carpets and furniture which reveals a
slight phosphorescent light in the dark where bloodstains (and
certain other stains) are present.
What is the luminol test?
The specialist will try to determine what the position and shape
of bloodstains at the crime scene indicate. He/she take measurements
to determine the trajectory as well as execute carefully controlled
experiments. These experiments will use surface materials like those
found at the scene to try to reproduce what has happened.
A leading authority on blood stain interpretation gives the
following tips to investigators:
- It is possible to determine the impact angle of blood on a
flat surface by measuring the degree of circular distortion of the
stain. In other words, the shape of the stain tends to change
depending upon the angle of impact which caused the stain. For
example, the more the angle decreases, the more the stain is less
circular and more long.
- Surface texture is one of the key components in determining
spatter type. The harder the surface is, the less spatter will
result. It is therefore extremely important to duplicate the
surface in a controlled test.
- When a droplet of blood hits a surface which is hard as well
as smooth, the blood usually breaks apart upon impact. This in
turn causes smaller droplets. The smaller droplets will continue
to move in the same direction as the original droplet.
One of the classic
murder cases in which blood evidence played an important, if
controversial part was the trial of Dr Sam Sheppard. The doctor's wife was found
dead in their Cleveland Ohio, home in July
1954. Her body, with
the head brutally battered by over thirty blows from a heavy object
was found in the master bedroom. The room, which had been
ransacked, was heavily spattered with blood, and a trail of stains
led down the stairs and out on to a terrace.
Dr Sheppard, who had been awakened from sleep on the living room sofa by his wife's
screams, claimed to have been knocked unconscious by an intruder as
he rushed upstairs. His behaviour was judged to have been suspicious, and there was
considerable prejudice against him, not least on account of his
alleged infidelity. He was sent for trial and found guilty of second degree murder, for
which he was sentenced to life imprisonment. The coroner had made much of
bloodstains on the pillow in the murder room, and a bloody imprint
which he suggested had been caused by a surgical instrument which
had served as the murder weapon. This instrument was never
specified, but the imputation was plain that Sheppard, himself a
doctor, had used it to murder his wife. The murder room
abounded in blood evidence which if properly examined would have led
to other conclusions. It was left to Dr Paul Leland Kirk, Professor of
Criminalistics at Berkeley, to make a thorough assessment of this evidence several months later in order
to reconstruct the murder.
As the bedroom ceiling showed no traces of blood, Kirk reasoned that the murder weapon had
been wielded in a more or less horizontal fashion. This was borne out by the
state of blood splashes on the walls, some of which had been flung
from the murder weapon as it was swung backward and forward to make
contact with the victim's head. Other blood spatters had
come directly from the battered head. The Professor carried out
experiments which suggested the most likely weapon to have caused
the pattern of blood splashes was a heavy flashlight. He also judged that the
murderer stood between the twin beds, having noted blood drops which
had been smeared into streaks on the right side of the victim's
bed. This interpretation was supported by blood free areas on two of the walls
behind the murderer which had been protected from flying blood
spatters by his body. A killer standing in that position must have swung the murder weapon
with his left hand - Dr Sheppard was neither left-handed nor
ambidextrous.
By implication, the murderer must have been thoroughly spattered with blood. Yet apart from a bloodstain
on the knee of Sheppard's trousers, which got there when he stood
close to the bed to take his wife's pulse, there was no evidence of
other blood staining on his clothes A number of factors
similarly pointed away from Dr Sheppard as the murderer - it was
certainly the case that the examination of the blood evidence had
been bungled in the first instance. There was no better
illustration of this than the admission during a second trial that
the trail of stains leading from the bedroom through the living room
and out on the terrace had not even been properly tested for human
origin, nor was blood groupings attempted. Professor Kirk's
interpretation of the blood evidence went a long way towards
securing Dr Sheppard's eventual freedom.
Film and television aficionados may recognise the recognise in this case the
opening premise of The Fugitive. Obviously the series would
have been a lot shorter with the help of a good bloodstain
expert.
Some common terms used in bloodstain pattern
interpretation.
- Angle of Impact -- The acute angle formed
between the direction of a blood drop and the plane of the surface it
strikes.
- Cast-Off Pattern -- A bloodstain pattern
created when blood is released or thrown from a blood-bearing object
in motion.
- Drip Pattern -- A bloodstain pattern which results
from blood dripping into blood.
- Flight Path -- The path of the blood drop, as it
moves through space, from the impact site to the target.
- Flow Pattern -- A change in the shape and
direction of a bloodstain due to the influence of gravity or movement
of the object.
- Impact Pattern -- Bloodstain pattern
created when blood receives a blow or force resulting in the random
dispersion of smaller drips of blood.
- Misting -- Blood which has been reduced to a
fine spray, as a result of the energy or force applied to it.
- Projected Blood Pattern -- A bloodstain pattern
that is produced by blood released under pressure as opposed to an
impact, such as arterial spurting.
- Spatter -- That blood which has been
dispersed as a result of force applied to a source of blood.
Patterns produced are often characteristic of the nature of the forces
which created them.
- Target -- A surface upon which blood has been
deposited.
- Transfer/Contact Pattern -- A bloodstain
pattern created when a wet, bloody surface comes in contact with a
second surface. A recognizable image of all or portion of the
original surface may be observed in the pattern.
- Wipe Pattern -- A bloodstain pattern created when an
object moves through an existing stain, removing and/or altering its
appearance.
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