Transcript Blood Spatter Analysis

Chapter 8 Blood and
Blood Spatter
By the end of this chapter you will be able to:
 explain the composition of blood
 describe the function of blood cells
 determine the blood type of a blood sample
 conduct a blood spatter analysis
 examine wounds and describe the nature of the
weapon
 find and process blood evidence
All Rights Reserved South-Western / Cengage Learning © 2009
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Forensic Science: Fundamentals & Investigations, Chapter 8
Genetic Terms to Remember
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Phenotype- a set of observable
characteristics of an individual
Genotype- the genetic constitution of an
individual
Homozygous- having two of the same gene
(either dominant or recessive)
Heterozygous- having one dominant and one
recessive copy of a gene
Forensic Science: Fundamentals & Investigations, Chapter 8
Introduction and History
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Blood typing can provide class evidence;
whereas DNA profiling can provide individual
evidence.
 A blood spatter pattern can give information
about the truthfulness of an account by a
witness or a suspect.
 It also can provide information about the origin of
the blood, the angle and velocity of impact, and
type of weapon used.
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Forensic Science: Fundamentals & Investigations, Chapter 8
Composition of Blood
 Whole blood carries cells and plasma—the fluid
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with hormones, clotting factors, and nutrients.
Shown above respectively:
 Red blood cells carry oxygen to the body’s cells
and carbon dioxide away.
 White blood cells fight disease and foreign
invaders and, alone, contain cell nuclei.
 Platelets aid in blood clotting and the repair of
damaged blood vessels.
Forensic Science: Fundamentals & Investigations, Chapter 8
How do you get your blood type?
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There are 4 major blood types and 2 different
antibodies:
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A,B, AB, and O
Anti-A and Anti-B
You get your blood type from your parents.
You can determine the possible blood types
for an individual if you know the blood types
of their parents.
Forensic Science: Fundamentals & Investigations, Chapter 8
How do you get your blood type?
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Your blood types is a phenotype, but some blood
types can have multiple genotypes.
Blood types A and B are dominant over O
(recessive), but A and B are co-dominant with each
other
Phenotype
Genotype
Antibodies
A
AA or AO
Anti-B
B
BB or BO
Anti-A
AB
AB
None
O
OO
Anti-B and Anti-A
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Proteins
42%
12%
3%
of the population in the United States
(of which 85% is Rh+)
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43%
Blood typing is quicker and less expensive than
DNA profiling.
 It produces class evidence but can still link a
suspect to a crime scene or exclude a suspect.
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Antibodies; Additional
Proteins and Enzymes
 Antibodies are proteins secreted by white
blood cells that attach to antigens to destroy
them.
 Antigens are foreign molecules or cells that
react to antibodies.
 Enzymes are complex proteins that catalyze
different biochemical reactions.
 Many enzymes and proteins have been found in
the blood that are important for identification
purposes.
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Probability and
Blood Types
 Given the frequency of different genes within a
population, it is possible to determine the
probability that a particular blood type will appear
in a particular population.
 To determine the probability of two separate
events, it is necessary to multiply their individual
probabilities.
 By identifying the additional proteins in the blood
evidence sample, investigators can limit the size of
a suspect population and help identify a suspect.
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Forensic Science: Fundamentals & Investigations, Chapter 8
Practice Probability
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A man who is heterozygous Type A marries and
woman who is heterozygous Type B. What are the
possible phenotypes and genotypes of their
children?
Genotype
Phenotype
B
O
AB
AB
A
AB
AO
AO
A
O
BO
OO
BO
B
OO
O
Forensic Science: Fundamentals & Investigations, Chapter 8
The Rh Factor
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Red blood cells carry proteins on their
surfaces in addition to anti-A and anti-B.
The Rhesus factor, Rh, is a protein carried by
some individuals.
If a person carries the Rh factor they are “Rh
positive.” If not, they are “Rh negative.”
Rh is a dominant trait, so only one copy of
Rh+ is need for a person to be Rh+.
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis
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http://www.youtube.com/watch?v=J40wqqg_
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter
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In 1939 the meaning of the spatter pattern was
first analyzed.
When a wound is inflicted, a blood spatter
pattern may be created.
It takes a grouping of blood stains to make a
blood spatter pattern.
The pattern can help to reconstruct the events
surrounding a shooting, stabbing, or beating.
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis
Analysis of a spatter pattern can aid in
determining the:
– direction blood traveled.
– angle of impact.
– point of origin of the blood.
– velocity of the blood.
– manner of death.
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter
Analysis
 When blood falls from a height or at a high
velocity, it can overcome its natural
cohesiveness and form satellite droplets.
 When it falls onto a less-than-smooth
surface, it can form spiking patterns around
the drops.
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis-Passive
Patterns
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Passive Drop- Bloodstain drop(s) created or formed
by the force of gravity acting alone
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis-Passive
Patterns
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Drip Pattern- A bloodstain pattern which results from
blood dripping into blood
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis-Passive
Patterns
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Flow Pattern- A
change in the shape
and direction of a
bloodstain due to the
influence of gravity or
movement of the
object
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis-Passive
Patterns
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Pool- a bloodstain pattern created when a source
of blood remains stationary over a surface
causing an accumulation of blood
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis-Passive
Patterns
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Saturation-A
bloodstain pattern
created when a
volume of blood has
been absorbed by
an object
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis-Transfer
Patterns
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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 a portion of the original surface may
be observed in the pattern
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis-Transfer
Patterns
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Swipe Pattern-The transfer of blood from a moving
source onto an unstained surface. Direction of travel
may be determined by the feathered edge
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis-Transfer
Patterns
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Wipe Pattern- A bloodstain pattern created when an
object moves through an existing stain, removing
and/or altering its appearance
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter AnalysisProjected/Impact Spatter
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Arterial Spurting- bloodstain pattern(s) resulting
from blood exiting the body under pressure from a
breached artery
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter AnalysisProjected/Impact Spatter
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Cast-off Pattern- a
bloodstain pattern created
when blood is released or
thrown from a blood-bearing
object
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter AnalysisProjected/Impact Spatter
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Expirated Blood- Blood that is blown out of the nose,
mouth, or a wound as a result of air pressure and/or
air flow which is the propelling force.
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter AnalysisProjected/Impact Spatter
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Low Velocity Impact Spatter (LVIS)- A bloodstain
pattern that is caused by a low velocity impact/force
to a blood source
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter AnalysisProjected/Impact Spatter
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Medium Velocity Impact Spatter (MVIS)- a
bloodstain pattern caused by a medium velocity
impact/force to a blood source.
A beating typically causes this type of spatter
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter AnalysisProjected/Impact Spatter
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High Velocity Impact Spatter (HVIS)- a bloodstain
pattern caused by a high velocity impact/force to a
blood source
Often produced by a gunshot or high speed
machinery
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter AnalysisMiscellaneous
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Void- an absence of stain in an otherwise continue
bloodstain pattern
Indicates that a person or object was in the way of
the blood spatter and was later moved
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter AnalysisMiscellaneous
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Skeletonized Stains- a bloodstain consisting of a
darkened peripheral rim where the center of the stain
is no longer intact
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis—
Directionality
The shape of an individual drop of blood
provides clues to the direction from where
the blood originated.
How will the point of impact compare
with the rest of a blood pattern?
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Droplet Characteristics
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A blood droplet will remain spherical in space
until it collides with a surface.
The spherical shape is caused by the surface
tension of the blood.
Forensic Science: Fundamentals & Investigations, Chapter 8
Angle of Impact
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The shape of a blood drop:
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Round- if it falls straight down at a 90 degree
angle
Elliptical- blood droplets elongates as the angle
decreases from 90 to 0 degrees
Forensic Science: Fundamentals & Investigations, Chapter 8
Determining the Angle of Impact
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Angle of impact= sin-1(width/height)
Forensic Science: Fundamentals & Investigations, Chapter 8
Determining Angle of Impact
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Make sure your calculator is
in degrees!
Example: Width= 3mm,
Length= 5mm
Angle= Sin-1(3mm/5mm)
Angle = 37 degrees
Forensic Science: Fundamentals & Investigations, Chapter 8
Origin of the Blood
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Lines of convergence
Draw straight lines down the axis of the
blood spatters.
Where the lines converge, the blood
originated.
Forensic Science: Fundamentals & Investigations, Chapter 8
Determining Point of Origin
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6.
Place the ring stand on area of convergence
Write the calculate angle of impact next to each
stain.
Using string, tape, and a protractor, raise the string
to the calculated angle and attach it to the ring
stand.
Do the same for multiple stains.
The place on the ring stand where the string from
each stain meets is the area of orgigin
Measure the height of the area of origin
Forensic Science: Fundamentals & Investigations, Chapter 8
Crime Scene Investigation
of Blood
Search for blood evidence.
2. If any is discovered, process it determining:
a. Whether the evidence is blood.
b. Whether the blood is human.
c. The blood type.
3. Interpret the findings:
a. See if the blood type matches a suspect.
b. If it does not, exclude that suspect.
c. If it does, decide if DNA profiling is needed.
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Forensic Science: Fundamentals & Investigations, Chapter 8
. . . . . . . . . . . . . . . . . Summary
 Blood consists of cellular components and plasma.
 The various human blood types are caused by the
presence or absence of A or B or both A and B
proteins on the surface of red blood cells.
 Blood splatter evidence can be used to recreate a
crime scene.
 Investigators endeavor to (a) locate, (b) identify,
and (c) interpret blood splatter patterns at crime
scenes.
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Forensic Science: Fundamentals & Investigations, Chapter 8