Transcript Blood - Marblehead High School

Chapter 8 Blood and
Blood Splatter
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 splatter 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
Introduction and History
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Blood typing can provide class evidence;
whereas DNA profiling can provide individual
evidence.
 A blood splatter 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.
 Our understanding of blood began in ancient
times and continues to grow today.
Forensic Science: Fundamentals & Investigations, Chapter 8
Composition of Blood
 Whole blood
carries cells and
plasma
– Plasma—(55%)
the fluid with
dissolved proteins
like antibodies,
hormones, clotting
factors, and
nutrients like
glucose, amino
acids, salts and
minerals.
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Forensic Science: Fundamentals & Investigations, Chapter 8
Composition of Blood
Cellular components of blood (45%):
 Red blood cells carry oxygen to the body’s cells
and carbon dioxide away, contain hemoglobin and
no nucleus.
 White blood cells fight disease and foreign
invaders and, alone, contain cell nuclei – used to
make first DNA profile in 1982
 Platelets are cell fragments that aid in blood
clotting and the repair of damaged blood vessels.
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Forensic Science: Fundamentals & Investigations, Chapter 8
The Composition of Blood
Platelets thrombocytes
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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
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Antibodies are proteins secreted by white blood cells
that attach to antigens to destroy them (not made to
attack our bodies own antigens).
Antigens are substances on the cell surface of red
blood cells (or foreign invaders)
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 Types
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Forensic Science: Fundamentals & Investigations, Chapter 8
Genetics - FUN STUFF!!!!
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Shows multiple alleles
Shows codominance
Genetics terms to know:
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Forensic Science: Fundamentals & Investigations, Chapter 8
Genes
Traits
Alleles – dominant vs.
recessive
Genotype – heterozygous
vs. homozygous
Phenotype
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
Blood Splatter
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In 1939 the meaning of the splatter pattern was
first analyzed.
When a wound is inflicted, a blood splatter
pattern may be created.
It takes a grouping of blood stains to make a
blood splatter pattern.
The pattern can 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:
– 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 Splatter
Analysis
•Blood is cohesive
•Gravity causes a drop of blood to
elongation as it falls
 When blood falls from a height or at a high velocity,
it can overcome its natural cohesiveness and form
satellite droplets (separates from the original).
 When it falls onto a less-than-smooth surface, it
can form spiking patterns around the drops, if not
it will have a curved surface due to surface tension
with smooth edges
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis—Six
Patterns
Describe each of these:
a. passive drops
b. arterial gushes
c. splashes
d. smears
e. trails
f. pools
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Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Spatter Analysis - Blood Drops
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Size & shape help identify the direction of
origin
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Round drops: 90 degree angle drop
Tails & Satellites: Indicate where the blood came
from (points of origin)
Blood drops lead away from the source
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis—Impact
Fine Mist
Patterns can help investigators determine the type of weapon
used.
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What kind of a pattern is produced by a gun shot?
What kind of a pattern is produced by a hammer blow?
Voids are used to indicate the presence of a person or
object
Forensic Science: Fundamentals & Investigations, Chapter 8
Blood Splatter Analysis—
Directionality
Points in the direction of movement
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—Location of the Origin of the
Blood
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Lines of convergence
Draw straight lines down the axis of the
blood splatters.
Where the lines converge, the blood
originated.
Forensic Science: Fundamentals & Investigations, Chapter 8
Crime Scene Investigation
of Blood
Search for blood evidence.
a. Luminol is used to detect the blood protein hemoglobin
even after an area has been cleaned of blood it will react
and generate light
2. If any is discovered, process it determining:
a. Whether the evidence is blood. - (1) Kastle-Meyer test turns pinks in the presence of blood or (2)
Lukomlalachite green test -turns green in the presesnce
of blood
b. Whether the blood is human - ELISA test
c. The blood type.
1.
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Forensic Science: Fundamentals & Investigations, Chapter 8
Crime Scene Investigation
of Blood
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