Chapter 8 Blood and Blood Splatter
By the end of this chapter you will be able to:
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Explain the composition of blood
Describe the function of blood cells
Determine the blood type of a blood sample
Conduct a blood splatter analysis
Examine wounds and describe the nature of the
weapon
Find and process blood evidence
All Rights Reserved South-Western / Cengage Learning © 2012, 2009
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Forensic Science: Fundamentals & Investigations, Chapter 8
Introduction and History
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Blood typing provides class evidence
DNA profiling provides individual evidence
A blood splatter pattern provides information
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the truthfulness of an account by a witness or a
suspect
the origin of the blood
the angle and velocity of impact
the type of weapon used
Forensic Science: Fundamentals & Investigations, Chapter 8
Composition of Blood
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Plasma—a liquid suspending other blood
components
Red blood cells (Erthrocytes)—carries oxygen to
the body’s cells and carbon dioxide away
White blood cells (Leukocytes)—fights disease
and foreign invaders and, alone, contain cell nuclei
Platelets—aids in blood clotting and the repair of
damaged blood vessels
Forensic Science: Fundamentals & Investigations, Chapter 8
Composition of Blood
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Forensic Science: Fundamentals & Investigations, Chapter 8
Types of Blood Cells
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Forensic Science: Fundamentals & Investigations, Chapter 8
Cellular Components of Blood
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Proteins
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Discovered in 1900 by Karl Landsteiner
Identifies the presence or absence of particular
proteins embedded in the cell
Quicker and less expensive than DNA profiling
Produces class evidence but can still link a
suspect to a crime scene or exclude a suspect
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Proteins
42%
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12%
3%
of the population in the United States
Forensic Science: Fundamentals & Investigations, Chapter 8
43%
Rh Factor
85% of the population has a protein called
RH factor on their blood cells
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing—Antibodies
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Antibodies are Y-shaped
proteins secreted by white
blood cells that attach to
antigens to destroy them
Antigens are foreign
molecules or cells that
react to antibodies
Forensic Science: Fundamentals & Investigations, Chapter 8
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Enzymes
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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
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Typing
—Probability and Blood Types
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The probability of a blood type equals the product of
probabilities for each protein group
If Type A = 42% and Rh Factor = 85%
Then A+ = .42 x .85 = .357 (35.7%)
Knowing additional proteins and enzymes in the
blood sample
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Narrows the population group
Increases the probability of identifying a suspect
Forensic Science: Fundamentals & Investigations, Chapter 8
Forensics of Blood
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The determination of blood is best
made by means of a preliminary color
test.
Blood Color Tests
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A positive result from the Kastle-Meyer
color test is highly indicative of blood.
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Hemoglobin causes a deep pink color.
Blood Color Tests
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Alternatively, the luminol test or
Bluestar test are used to search out
trace amounts of blood located at crime
scenes.
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Produces light (luminescence) in a
darkened area.
Luminol is extremely sensitive and is
capable of detecting blood that has been
diluted up to 100,000 times.
Blood Origin Testing
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Once the stain has been characterized
as blood, the precipitin test will
determine whether the stain is of
human or animal origin.
The precipitin test uses antisera
normally derived from rabbits that have
been injected with the blood of a
known animal to determine the species
origin of a questioned bloodstain.
Blood Origin Testing
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The technique of gel diffusion takes
advantage of the fact that antibodies
and antigens diffuse or move toward
one another on an agar plate.
The extracted bloodstain and the
human antiserum are placed in
separate holes opposite each other on
the gel. If the blood is human, a line of
precipitation forms where the antigens
and antibodies meet.
FIGURE 14–6
test.
The precipitin
FIGURE 14–7
Antigens and
antibodies moving toward one another under the influence of an
electrical potential.
Blood Splatter
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1939—splatter patterns first
analyzed
Blood may splatter when a wound is inflicted
Blood splatter pattern—a grouping of blood
stains
Patterns help to reconstruct the events
surrounding a shooting, stabbing, or beating
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis
Analysis of a splatter pattern can aid in
determining the:
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direction blood traveled
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angle of impact
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point of origin of the blood
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velocity of the blood
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manner of death
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis
Natural cohesiveness of blood
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis
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Satellite droplets—
• When blood falls from a height, or at a high velocity,
• It overcomes its natural cohesiveness, and
• Separates from the main droplet
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Spiking patterns—
• Form around the droplet
edges when blood falls
onto a less-than-smooth
surface
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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 Splatter Analysis
Lines of convergence—two or blood splatters can
pinpoint the location of the blood source
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis
—Six Patterns
Describe each of these:
a)
b)
c)
d)
e)
f)
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Passive drops
Arterial gushes
Splashes
Smears
Trails
Pools
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis
—Impact
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Patterns can help investigators determine
the type of weapon used
What kind of a pattern is produced by a gun
shot?
What kind of a pattern is produced by a
hammer blow?
Forensic Science: Fundamentals & Investigations, Chapter 8
Crime Scene Investigation
of Blood
1. Search for blood evidence
2. Determine
a. Is the evidence blood?
b. Is the blood human?
c. What is the blood type?
3. Interpret the findings:
a. Does the blood type match a suspect’s blood?
b. If not, exclude that suspect
c. If yes, decide if DNA profiling is necessary
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Forensic Science: Fundamentals & Investigations, Chapter 8
. . . . . . . . . . . . . . . . . Summary
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Blood consists of cellular components and plasma.
The various human blood types are caused by the
presence or absence of A and/or 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.
Forensic Science: Fundamentals & Investigations, Chapter 8