FORENSIC SCIENCE Serology

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Having sniffed the dead mans lips, I detected a
slightly sour smell, and I came to the conclusion
that he had poison forced upon him. Sherlock
Holmes, in Sir Arthur Conan Doyles A Study in
Scarlet
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Blood evidence

• Blood typing can provide _____ evidence DNA
  profiling can provide __________ evidence.
• What information can be obtained from blood
  spatter?

class
individual

• information about the origin of the blood
• the angle and velocity of impact
• type of weapon used
• the truthfulness of an account by a witness or a
  suspect

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Serology

• Serology is the examination
  and analysis of body fluids (saliva, semen,
  urine, and blood.)
• Through the late 1980s, forensic serology was a
  most important part of lab procedures. With the
  development of DNA techniques, more time, money,
  and significance was placed in developing DNA
  labs.
• Blood typing is quicker and less expensive than
  DNA profiling.

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Blood Characteristics

• Plasma - the fluid portion of the blood (55)
• Cells (45)
• Erythrocytes (red blood cells) most numerous -
  carry oxygen and CO2 and have proteins that ID
  blood type
• Leukocytes (white blood cells) contain cell
  nuclei and fight disease/foreign invaders used
  for DNA
• Thrombocytes (platelets) are responsible for
  blood clotting

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Unknown Stain at a Scene

• Questions to be answered
• Is it blood?
• Is it human blood?
• Whose is it?
• Determine blood type, alcohol content, drugs
  present
• Determine the method(s) in which blood may have
  been deposited

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Human vs Animal Blood

• Microscopic observation
• Precipitin test
• human blood is injected into a rabbit
• antibodies form
• the rabbits blood is extracted as an antiserum
• the antiserum is placed on sample blood
• The sample will react with human proteins if
  human blood is present.
• This test is very sensitive and requires only a
  small amount of blood.

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Blood Terminology

• ABO blood groupsbased on having an A, B, both or
  no antigens on red blood cells
• Rh factormay be present on red blood cells
  positive if present and negative if not
• Antigena substance that can stimulate the body
  to make antibodies. Certain antigens (proteins)
  found in the plasma of the red blood cells
  membrane account for blood type.
• Antibodya substance that reacts with an antigen
• Agglutinationclumping of red blood cells will
  result if blood types with different antigens are
  mixed

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Blood Typing

• Blood type A has antigen A on the surface of the
  cell and will agglutinate with blood type B.
• Blood type B has antigen B on the surface of the
  cell and will agglutinate with blood type A.
• Blood type AB has antigens A and B on the
  surface of the cells and will not agglutinate
  with either type A or B blood.
• Blood type O has neither antigen A or B and will
  not agglutinate.

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Blood Groups
Can Give Blood To
Can Get Blood From
Antigen
Type
Antibody
A
B
AB
O
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Population Distribution of Blood Types in the
U.S.
Type
Percent
O
45
A
41
B
10
AB
4
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Blood Droplet Characteristics

• A blood droplet will remain spherical in space
  until it collides with a surface
• Once a blood droplet impacts a surface, a
  bloodstain is formed.
• A droplet falling from the same height, hitting
  the same surface at the same angle, will produce
  a stain with the same basic shape.

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Conditions Affecting Shape of Blood Droplet

• Size of the droplet
• Angle of impact
• Velocity at which the blood droplet left its
  origin
• Height

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Blood Spatter Interpretation

• 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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Impact

• 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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Blood Splatter Analysis Six Patterns
Splash smear passive drop
Describe and ID each of these a. passive drops
b. arterial gushes c. splashes d. smears
e. trails f. pools
trail
Pool arterial gushes
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Blood Splatter Analysis Impact

• 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?

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Bloodstain Patterns

• The harder and less porous the surface, the less
  the blood drop will break apart.
• The softer and more porous the surface, the more
  a blood drop will break apart.
• The pointed end of the blood stain faces the
  direction of travel.

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Area of Intersectionand Convergence

• Draw straight lines down the axis of the blood
  splatters.
• Where the lines converge, the blood originated.

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Blood Evidence

• Blood stain patterns are considered
  circumstantial evidence in a court room.

• Experts could argue many points including
  direction of travel, height of the perpetrator,
  position of the victim, left/right hand, whether
  the body was moved, etc.

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Crime Scene Investigation of Blood

• Search for blood evidence.
• If any is discovered, process it determining
• Whether the evidence is blood.
• Whether the blood is human.
• The blood type.
• Interpret the findings
• See if the blood type matches a suspect.
• If it does not, exclude that suspect.
• If it does, decide if DNA profiling is needed.

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