Download 11.1 Introduction to Bloodstain Pattern Analysis

Introduction to
Bloodstain Pattern Analysis
“Art in the blood is liable to take the strangest forms.”
Sir Arthur Conan Doyle (1893)
Sherlock Holmes, The Adventure of the Greek Interpreter
Objectives
At the end of this lesson, students should be able to…
⚫ Define bloodstain pattern analysis (BPA) and its
associated terms
⚫ Explain why BPA is a useful forensic tool
⚫ Describe the physical characteristics of blood
⚫ Know the different types of bloodstain patterns
⚫ Discuss how to document and collect bloodstain
evidence
⚫ Understand the limitations of pattern recognition
and the limitations of BPA as a science
What is Bloodstain Pattern Analysis?
Bloodstain Pattern
Analysis (BPA)
The science that
uses the physical
appearance and
spatial distribution of
static bloodstains to
establish a timeline
of the events that
lead to their
deposition
What is Bloodstain Pattern Analysis?
Primary Functions of BPA:
1. To define or categorize
specific stains and patterns
found at a crime scene
2. To attempt to identify the
nature of the events that
caused the patterns
Unlike other types of evidence,
bloodstain patterns can
provide information about what
happened at a crime scene
Why is BPA Useful as a Forensic Tool?
The shape of
an individual
stain
indicates the
angle of
impact
Bloodstains
vary in
shape and
size
The size of an
individual stain
indicate the
force used to
create that stain
As the force
exerted on a
blood source
increases, the
resulting stains are
smaller and more
spread out
Why is BPA Useful as a Forensic Tool?
Analysts look at
stains
collectively and
evaluate the
patterns with
respect to each
other
Helps to indicate
the relative
positioning of the
suspect, victim,
and other related
objects during the
incident
Distribution of
bloodstains
Example:
Was the victim
standing up or
lying on the floor
when he was
attacked?
Why is BPA Useful as a Forensic Tool?
Experiments!
Blood behaves
similarly under
the same type of
circumstances
Bloodstains
are
reproducible
Why is BPA Useful as a Forensic Tool?
Once outside of the body,
blood obeys certain
predictable physical laws
Conducting experiments
can help provide a variety
of information about the
incident that occurred.
Types of Information:
Amount and type of force;
approx. number of blows
struck; positioning of
persons involved;
mechanism that created
the pattern; etc.
Physical Characteristics of Blood
• Volume
• Shape and surface tension
• Impact on a target surface
What Can Bloodstains Tell Us?
The volume
of a drop of
blood in flight
will always
remain the
same
What Can Bloodstains Tell Us?
Blood droplets will not break up
spontaneously during flight
Drops of blood will retain their
shape until acted upon by
some other force
The size of a drop of blood is
dependent on its volume
Click on photo to link to video clip.
Physical Characteristics of Blood
As a result of
surface tension,
a blood droplet
retains a
spherical shape
while in flight
Physical Characteristics of Blood
The liquid is forced to occupy a
sphere (smallest space possible)
because the surface tension
(molecular bonding force) on the
surface of the droplet is
stronger than the bonding
force within the mass of liquid
Damping is the process by
which a blood droplet in flight
stabilizes almost immediately
Physical Characteristics of Blood
The target
surface is the
most critical
element involved
in the
appearance of
the resulting stain
Physical Characteristics of Blood
The distortion of a stain may
eliminate an analyst’s ability to
decipher anything of value from
the blood evidence
For example, blood on carpet or
fabric is absorbed by the surface,
distorting the stain
Smooth surfaces produce the best
bloodstain patterns
What Can Bloodstains Tell Us?
• Directionality
• Angle of Impact
• Area of Origin
• Distance
What Can Bloodstains Tell Us?
Directionality:
The direction a
blood drop was
traveling at the
time it impacted
a surface
What Can Bloodstains Tell Us?
Inertia caused by the motion of
the droplet forces a wave of
blood to form, which then wells up
on the opposite point from where
the stain struck the surface
The leading edge of the blood
droplet impacts first and the blood
runs in the direction of travel
The tail of the bloodstain always
points in the direction of travel
What Can Bloodstains Tell Us?
Inertia caused by the motion of
the droplet forces a wave of
blood to form, which then wells up
on the opposite point from where
the stain struck the surface
The leading edge of the blood
droplet impacts first and the blood
runs in the direction of travel
The tail of the bloodstain always
points in the direction of travel
What Can Bloodstains Tell Us?
Angle of
Impact:
The angle at
which a blood
drop strikes a
surface
What Can Bloodstains Tell Us?
The greater the angle of impact, the more circular the resulting bloodstain.
What Can Bloodstains Tell Us?
The greater the angle of impact, the more circular the resulting bloodstain.
What Can Bloodstains Tell Us?
Area of Origin:
The approx.
area above the
target surface
from which the
drop originated
What Can Bloodstains Tell Us?
3D location in space – the stains radiate out from the area of origin
What Can Bloodstains Tell Us?
Distance:
The approx.
distance above
the target
surface where
the stain
originated
What Can Bloodstains Tell Us?
Helps to determine the
location of the origin of the
blood source
Due to air resistance,
terminal velocity for a drop
of blood occurs at a
distance of approx. 7 feet
You can only determine
conclusively the distance a
drop of blood has fallen if
you know the volume of the
drop
Bloodstain Pattern Categories
• Passive
• Transfer
• Projected or impact
•
Types of force
• Miscellaneous
Bloodstain Pattern Categories
Drops,
flows,
pools,
and clots
Passive
Stains
Provides information
about when the
bloodshed occurred
and any disturbances
that happened after
the bloodshed
Bloodstain Pattern Categories
Drop:
Often
referred to as
passive
bleeding or
low velocity
spatter
Click on photo to link to video clip.
Bloodstain Pattern Categories
The more quickly a blood
source is moving, the greater
the distance between the
drops of blood
The tails on drops of blood can
tell the direction in which the
actively dripping blood source
was moving at the time of
deposition
Satellite spatter result from the
deposition of small droplets
that are ejected from the
blood pool when it’s struck by
a falling drop
Click on photo to link to video clip.
Bloodstain Pattern Categories
Passive
Flow:
Created by
gravity alone,
and does not
involve
circulatory
action
Blood Pool:
Pattern occurs
when
gravitational
forces pull blood
to the lowest
possible level, and
the blood
accumulates
Bloodstain Pattern Categories
The blood flow takes
the path of least
resistance
Helps to indicate whether
items at a crime scene have
been moved
Saturation stains occur
when a surface absorbs
a quantity of blood
Bloodstain Pattern Categories
Clot:
Blood that has
undergone the
physiological
process of fibrin
formation that
congeals the solid
elements of blood
into a gelatinous
mass
Bloodstain Pattern Categories
Patterns,
swipes,
and wipes
Result when a
bloody object
comes into
contact with
another
surface
Transfer
Stains
Provides info about:
• Movement of the
victim or suspect
• Sequence of
events
• Identification of
weapons
Bloodstain Pattern Categories
Pattern
Transfer:
Created when a
wet bloody object
comes into
contact with
another surface
Bloodstain Pattern Categories
The resulting pattern may
provide specific characteristics
that help to identify the object
Bloodstain Pattern Categories
Swipe:
Results when a
bloody object
comes into
contact with a
clean surface
Provides indication of movement
within the crime scene
Bloodstain Pattern Categories
Wipe:
Results when a
non-bloody
object comes
into contact
with a bloody
surface
Provides indication of movement
within the crime scene
*** this wipe also has skeletonization ***
Bloodstain Pattern Categories
Projected
blood,
spatter, castoff, and
splashes
Projected
& Impact
Stains
Provides info about:
• Type or nature of
force used
• Staging of scene
• Min. number of
blows (blunt force)
• Movement of the
victim
Bloodstain Pattern Categories
Projected
Blood:
Produced when
blood, released
under pressure,
impacts a
surface
Bloodstain Pattern Categories
Normally associated with
arterial spurts and gushes –
traumatic bleeding from
vessels under pressure – and
typically has a linear pattern
Bloodstain Pattern Categories
Spatter:
The result of
force being
applied to a
blood source
Bloodstain Pattern Categories
The greater the force, the smaller
the resulting blood drops, and
the wider the distribution of the
resulting stains
Spatter is distributed randomly,
varies in size, and is produced by
a variety of mechanisms
Types of Force
Size:
4mm or
larger
Low Velocity:
Results from
normal
gravitational
force of up to 5
feet/sec.
Typical of
venus
bleeding
(blood under
low pressure)
Types of Force
The size of the blood spatter is relatively large, because the energy
applied to the blood source is limited, minimizing the degree to
which the blood drops break apart
Blood stains are often associated with blood dripping from an injury
or weapon
Types of Force
Size:
Approx.
1mm to
4mm
Medium
Velocity:
Results from force
or energy
between 5 and
25 feet/sec.
Typical of
injuries
resulting from
blunt force
trauma
Types of Force
Blood droplets are broken up as a result of
increasing energy applied to the blood source
Typically associated with beatings and stabbings
Bloodstain Pattern Categories
Cast-Off:
Created when
blood is flung or
projected from
an object in
motion, or when
that motion
stops suddenly
Bloodstain Pattern Categories
Arc cast-off patterns are
characterized by linear
patterns, typically found on
the ceiling or walls
The objects casts off blood
droplets as it arcs through
the air
Cessation/stop-action
cast-off patterns are
created by a bloodbearing object is stopped
abruptly
Bloodstain Pattern Categories
The directionality of castoff patterns in relation to
the area of origin may
provide information about
which hand the offender
used during the attack
May be used
(with caution) to estimate a
minimum number of blows
in blunt force trauma
Help to reconstruct the
series of events and
locations of those involved
Types of Force
Size:
Mist-like;
1mm or
smaller
High Velocity:
Results from force
or energy in
excess of 100
feet/sec.
Typical of
gunshot
wounds, high
powered
machinery
injuries, and
explosions
Types of Force
Bullet hole
Types of Force
Bullet hole
Back spatter are bloodstains that are projected
towards the item creating the force or energy.
For example, when a bullet is fired from a gun and hits a bloody
surface, blood not only travels in the direction of the bullet, but also
travels backwards onto the gun.
Bloodstain Pattern Categories
Expirated
Blood:
Blood which is
spattered on a
target from the
mechanical
process of
breathing
Bloodstain Pattern Categories
Expirated blood
accumulates in the lungs,
sinuses, and airway, and
may be mixed with saliva or
nasal secretions
These stains often include
air bubbles.
Because expirated blood
tends to form a fine mist
due to the pressure exerted
by the lungs moving air out
of the body, it may be
mistaken for high velocity
spatter
Bloodstain Pattern Categories
Splash:
Pattern
created when
a volume of
blood impacts
a surface with
minimal force
Bloodstain Pattern Categories
Typically associated with a
staged crime scene, where
blood has been poured on a
surface
Bloodstain Pattern Categories
Voids,
skeletonization,
and expirated
blood
Miscellaneous
Stains
Provides info about:
• Movement at the
scene
• Timing of events
• Sequence of
events
Bloodstain Pattern Categories
Voids:
An empty
space found in
the middle of
an otherwise
bloody surface
Bloodstain Pattern Categories
Voids are useful for
determining the positioning
of items during the event.
For example, a void may be
indicative that a door was
open during the attack or
that an item is missing from
the scene.
Bloodstain Pattern Categories
Fly Spots:
Regurgitation,
excretion, or
tracking of minute
amounts of blood
around a scene or
onto items a within
the scene
Bloodstain Pattern Categories
May be mistaken for spatter,
but is not actually a result of
the bloodshed
Bloodstain Pattern Categories
Skeletonization:
Occurs when a
blood stain, which
has begun to dry,
is disturbed
Bloodstain Pattern Categories
Blood dries from the outside
inward, so when an object
goes through a bloodstain that
is still wet, the skeleton of the
stain remains.
Drying time is dependent upon
the surface on which the
blood is deposited and the
environmental conditions
Documentation and Collection
Limitations of BPA
Documentation and Collection
Photography
and sketches
Follow standard
crime scene
processing
procedures to
locate and
adequately
document all
blood evidence
Stringing
Documentation and Collection
Photographs:
It is critical to take
the close-up
photographs at a
90° angle to the
evidence to avoid
distortion
Scales
Bloodstain
Photo taken from 90° angle
Documentation and Collection
Sketches:
Cross-projection
sketches are most
useful because
bloodstain scenes
need to be
viewed in more
than one
dimension
Documentation and Collection
Cross-projected sketches are
helpful in showing the
relationships between various
groups of stains. These stains
exist on different surfaces,
including objects in the room,
floors, walls, and the ceiling
Documentation and Collection
Stringing:
Used to provide
a graphic 3D
illustration of the
areas of origin of
bloodstains
Documentation and Collection
Practically speaking, stringing is
useful for determining whether a
victim was standing, lying down,
or sitting in a chair when the
bloodshed occurred
It is important to remember
that stringing is not an exact
science, and only provides an
estimation of the area of origin
Limitations of BPA
Requires significant
experience and training
Ability to interpret
bloodstains
Ability to provide
effective
testimony in court
Analysis should not be
conducted with a
limited number of stains
Information available
through BPA is
dependent upon the
circumstances found at
a crime scene
The greater the
number of stains,
the greater the
potential for
accurate
assessment of
the scene
The messier the
crime scene, the
more information
that is available
to analysts
Limitations to Pattern Recognition
Environmental
Factors
Post-Event
Artifacts
Quality of
Scene
Information
Ancillary
Information
Temperature
Offender
activity
Photographs
Medical
and/or
autopsy
reports
Humidity
Medical
intervention on
scene
Measurements
Lab reports
Civilian and
first responder
activity
Control of
scene
Individual
statements
(suspect,
victim, etc.)
Animal and
insect activity
Press reports
Limitations to Pattern Recognition
Environmental
Factors
Post-Event
Artifacts
Quality of
Scene
Information
Ancillary
Information
Temperature
Offender
activity
Photographs
Medical
and/or
autopsy
reports
Humidity
Medical
intervention on
scene
Measurements
Lab reports
Civilian and
first responder
activity
Control of
scene
Individual
statements
(suspect,
victim, etc.)
Animal and
insect activity
Press reports
BPA only provides parameters for the investigator –
there are few absolutes in bloodstain pattern interpretation