Download Chapter 8 Blood and Blood Splatter

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
Introduction and History
• Blood typing can provide __________________________ evidence; whereas
•
DNA profiling can provide _____________________________ 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
•
Our understanding of blood began in ancient times and continues to grow
today.
Composition of Blood
• Whole blood carries cells and plasma—
•
Red blood cells carry
o White blood cells
o Platelets aid in
Blood Typing—Proteins
42%
12%
3%
43%
of the population in the United States
(of which 85% is Rh+)
•
Blood typing is
1
•
It produces class evidence but can still link a suspect to a crime scene or exclude a
suspect.
Blood Typing—Antibodies; Additional Proteins and Enzymes
• Antibodies are
•
Antigens are
•
Enzymes are
•
Many enzymes and proteins have been found in the blood that are important
for identification purposes.
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.
Blood Splatter
• In 1939 the meaning of the splatter pattern was first analyzed.
•
•
•
The pattern can help to reconstruct the events surrounding a shooting,
stabbing, or beating.
Laws of Physics
• All fluids follow the laws of physics
• What Forces affect falling objects?
• Newton’s Laws of Motion???
• Falling
o
o
o

in the case of any fluid containing a high % of H2O
2
Newton’s 1st Law of Motoin
• Resists changing motion until a force is applied
o
o
Newton’s 2nd Law
• Force applied is proportional to Acceleration achieved
• F = mass x acceleration
• Work done = F x distance fallen
o
o
•
Greater work weakens surface tension
•
Flatter stain from reducing surface tension
o
Newton’s 3rd Law
• Action and Reaction
•
Blood Splatter Analysis
• Analysis of a splatter pattern can aid in determining the:
o
o
o
o
o
Blood Splatter Analysis
• When blood falls from a height or at a high velocity,
•
When it falls onto a less-than-smooth surface,
3
Blood Splatter Analysis—Six Patterns
•
•
•
•
•
•
Impact
• Patterns can help investigators determine
•
•
•
Calculate with two measurements
Length of satin and width of stain
Impact Angle θ = sin -1 (width/length)
W
L
Speed/Velocity
•
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?
Location of the Origin of the Blood
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Lines of convergence
a. Draw straight lines down the axis of the blood splatters.
b. Where the lines converge, the blood originated.
Crime Scene Investigation of Blood
1. Search for blood evidence.
2. If any is discovered, process it determining:
a.
b.
c.
3. Interpret the findings:
a.
b.
c.
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