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Forensic Science
A. History of Blood
a. 2500 B.C. – Egyptians used bloodletting to try to cure diseases
b. 500 B.C. – Greeks distinguished between arteries and veins
c. 1659 A.D. – Anton van Leeuwenhoek viewed blood cells under a microscope
d. 1795 – First blood transfusion performed
e. 1901 – Karl Landsteiner discovered three blood types: A, B, O
f. 1902 – Alfred Decastello discovered fourth blood type: AB
g. 1922 – Percy Oliver established the first blood donor service
h. 1935 – Mayo Clinic developed a method to store blood for transfusions
i. 1937 – Dr. Bernard Fantus established the first blood bank
j. 1940 – Karl Landsteiner discovered the Rh protein
k. 1959 – First case of AIDS recorded in the Congo
l. 1984 – Robert Gallo identified the virus causing AIDS
m. 1985 – Development of ELISA test to screen for diseases such as HIV
n. 1987 – Scientists began developing blood-screening tests for infectious diseases
B. Study of Blood
a. Forensic Serology is the study of blood applied to crime.
b. Blood can provide various evidence to investigators at a crime scene:
i. Blood spatter patterns can be used to reconstruct a crime scene and show how an attack was
ii. Blood can connect an object with a crime (ex. Discarded weapon)
iii. Blood can connect a suspect with a crime (ex. blood on clothing) or place a suspect at a crime
scene (ex. Crimal blood at scene)
1. Blood typing is considered class evidence and is good to rule out suspects
2. DNA profiling from blood is considered individual evidence and can help pinpoint a
C. Composition of Blood
a. Blood is a tissue that circulates around through the body.
b. The average adult has about 10 pints of blood.
c. Blood is made of both cells (45%) and Plasma (55%)
d. There are 3 kinds of cells which make up blood:
i. Red Blood Cells (RBCs)
1. RBCs are called erythrocytes.
2. They have hemoglobin and carry oxygen and carbon dioxide.
a. Hemoglobin is an iron-containing protein that binds to oxygen and gives blood
its red color
3. They have no nucleus and no nuclear DNA.
ii. White Blood Cells (WBCs)
1. WBCs are called leukocytes.
2. They are an immune system cell, produced in bone marrow, which fight disease and
produce antibodies. There are many types of WBCs.
3. They are the only blood cells that contain DNA; therefore they are the only blood cell
useful in DNA profiling.
iii. Platelets
1. Platelets are called thrombocytes.
2. They are small cell fragments that assist in blood clotting and repair damaged blood
e. Plasma
i. Plasma is made of 90% water. The other 10% are:
1. Dissolved proteins (antibodies, hormones, clotting factors)
2. Nutrients (O2, glucose, amino acids, salts, minerals)
3. Wastes (urea, CO2)
D. Blood Types
a. Blood Typing identifies the presence or absence of particular proteins
embedded in the cell
b. It is quicker and less expensive than DNA profiling
i. Produces class evidence but can still link a suspect to a crime
scene or exclude a suspect
c. The presence or absence of cell-surface proteins determines a person’s
blood type.
d. A and B proteins
i. A and B proteins are found on the surface of some RBCs.
ii. If a person’s blood cells have A proteins, they have type A blood
iii. If a person’s blood cells have B proteins, they have type B blood
iv. If a person’s blood cells have both A and B proteins, they have
type AB blood
v. If a person’s blood cells have neither A nor B proteins, they have type O blood
e. Rh factor
i. 85% of the population has an additional surface protein called the Rh factor and therefore have
Rh positive blood.
ii. The other 15% lacks this protein and has what we call Rh negative blood.
iii. Referred to as Rh because it was first discovered in 1940 in Rhesus monkeys.
Antigen-antibody response
i. When a foreign material enters your body, your immune system launches
an attack called an antigen-antibody response in which WBCs called Blymphocytes release antibodies to attack the foreign substance.
1. Antibodies are Y-shaped proteins secreted by white blood
cells that attach to antigens to destroy them
2. Antigens are foreign molecules or cells that react to
a. Viruses, bacteria, and the RBCs of someone with a different
blood type all have antigen proteins that can cause an antigenantibody response.
ii. Blood typing is critical for blood transfusions. If a person receives a blood
protein foreign to their body, antibodies can cause the blood to clump which
possibly lead to death.
1. The clumping of RBCs is called agglutination.
2. Blood typing tests identify the presence of A, B, and Rh surface proteins.
g. Unique blood proteins
i. Many other blood proteins have been identified. Examples include M, N, PGM, AK, ADA. EsD, G6-PD, Gc, and Hp.
ii. These blood proteins can be very helpful in identification of blood at a crime scene.
iii. By testing for more blood proteins, the probability of uniqueness increases, making blood
evidence more individualized.
E. Blood Spatter
a. What is blood spatter?
i. A grouping of blood stains constitutes a blood splatter pattern.
ii. Patterns help to reconstruct the events surrounding shootings, stabbings, beatings, etc.
iii. In 1939, Dr. Victor Balthazard first researched and analyzed splatter patterns.
iv. Analysis of a splatter pattern can help to determine:
1. direction blood traveled
2. angle of impact
3. point of origin of the blood
4. velocity of the blood
5. manner of death
b. How blood falls and spatters
i. Cohesion
1. Blood sticks together as it falls maintaining a round shape.
2. Blood also resists flattening out when it falls on a flat
surface. Cohesion and surface tension help it to
maintain a curved shape.
ii. The shape of an individual drop of blood can provide important clues in an investigation
1. When blood falls from a height, or at a
high velocity, it overcomes its natural
cohesiveness, and separates from the
main droplet causing the formation of
satellite droplets, small secondary
droplets around the main drop.
2. When blood falls onto a less-than-smooth
surface, the edges may have spikes or
3. A circular drop of blood indicates a blood
drop fell straight down, without force. This is typical from a dripping wound.
4. An elongated blood drop indicates blood was traveling from a different direction when
it landed.
a. The point of impact may appear darker and wider than the rest of the drop,
with a tail pointing in the direction of the blood’s movement.
b. Smaller, secondary droplets may break off and will land in front of the moving
droplet of blood, allowing scientists to determine direction of spatter.
iii. When there are two or more blood splatters a scientist can draw lines of convergence that can
pinpoint the location of the blood source.
c. Different kinds of blood spatter
Passive drops
Arterial gushes
d. Speed and velocity also impact blood spatter
Size of blood droplets:
High Velocity
Medium Velocity
Low Velocity
Gunshot wound
Beating, stabbing
Blunt object impact
Less than 1 mm
1-4 mm
4-6 mm
F. Blood Evidence at a Crime Scene
a. Search for blood
i. Don’t see any blood?
1. Even with the most thorough cleaning, blood leaves
residue that is difficult to remove.
2. Luminol powder mixed with hydrogen peroxide is able to
detect hemoglobin left behind by blood. Spray the area
and if blood is present it will luminesce for about 30
3. Luminol reacts to old or new blood, however it destroys
the blood so it cannot be tested later.
ii. See blood?
1. If blood stains or drops are found, confirm they are in fact blood
a. There are many chemicals to test for the presence of blood.
i. Kastle-Meyer Test- swab turns pink if blood is detected
2. When possible, deliver blood or stained object to lab immediately.
3. If unable to deliver to the Laboratory, or if the object must be mailed, allow the stain to
air dry completely before packaging.
4. Blood that is in pools should be absorbed by a gauze pad and allowed to air dry. After it
dries it should be refrigerated or frozen as soon as possible. Blood should be taken to
the lab as quickly as possible; delays beyond 48 hours may make the samples useless.
5. If not completely dry, label and roll in paper or place in a brown paper bag or box and
seal and label container. Place only one item in each container. Do not use plastic
b. If blood is present, lab will need to confirm it is human blood.
i. Under a microscope you can tell if fresh blood is from a mammal.
1. All mammals, except camels and llamas, have circular, un-nucleated RBCs.
2. Animals that are not mammals (birds, fish, etc.) have oval blood cells with a nucleus.
ii. ELISA test uses antibodies that react to human blood to tell if mammal blood is from human.
However in rare cases, it can be confused with chimpanzee and gorilla blood.
c. If blood is human, try to determine whose blood it is. First test for blood type. If individual information is
needed, then do DNA analysis.