Blood. Objectives. You will understand: That an antibody and an antigen of different types will agglutinate, or clump, when mixed together. That the significance of the evidence depends on a characteristic’s relative occurrence in the population. Objectives, continued.
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You will understand:
That an antibody and an antigen of different types will agglutinate, or clump, when mixed together.
That the significance of the evidence depends on a characteristic’s relative occurrence in the population.
You will be able to:
Determine whether a stain is blood.
Determine whether a bloodstain is human or animal blood.
Determine the blood type of a simulated bloodstain using the ABO/Rh system.
Explore bloodstain patterns as a function of velocity, direction, and height of fall.
Use technology and mathematics to improve investigations and communications.
Serology is the examination and analysis of body fluids.
A forensic serologist may analyze a variety of body fluids including saliva, semen, urine, and blood.
From 1950 to the late 1980s, forensic serology was a most important part of lab procedures. With the development of DNA techniques, more time, money, and significance were placed on developing DNA labs. However, with limited funds and the time required for DNA testing, most labs still use many of the basic serology testing procedures.
Blood typing can provide class evidence; whereas DNA profiling can provide individual evidence.
A blood spatter 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.
Plasma is the fluid portion of the blood (55 percent).
Cells (45 percent)
Erythrocytes are red blood cells. They are responsible for oxygen distribution.
Leukocytes are the white blood cells; they are responsible for “cleaning” the system of foreign invaders.
Thrombocytes or platelets are responsible for blood clotting.
Serum is the liquid that separates from the blood when a clot is formed.
Whole blood carries cells and plasma—the fluid with hormones, clotting factors, and nutrients.
Shown above respectively:
Red blood cells carry oxygen to the body’s cells and carbon dioxide away.
White blood cells fight disease and foreign invaders and, alone, contain cell nuclei.
Platelets aid in blood clotting and the repair of damaged blood vessels.
Around 1900, Karl Landsteiner discovered that there are four different types of human blood based on the presence or absence of specific antigens found on the surface of the red blood cells.
In 1940, Landsteiner and Weiner reported the discovery of the Rh factor by studying the blood of the Rhesus monkey. 85 percent of Caucasians, 94 percent of Black Americans, and 99 percent of all Asians are Rh positive.
ABO blood groups—based on having A, B, both, or no antigens on red blood cells
Rh factor—may be present on red blood cells; positive if present and negative if not
Antigen—a substance that can stimulate the body to make antibodies. Certain antigens (proteins) found in the plasma of the red blood cell’s membrane account for blood type.
Antibody—a substance that reacts with an antigen
Agglutination—clumping of red blood cells; will result if blood types with different antigens are mixed
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
Kastle-Meyer color test—a mixture of phenolphthalein and hydrogen peroxide; the hemoglobin will cause the formation of a deep pink color if blood is present
Hematest tablet—reacts with the heme group in blood, causing a blue-green color
Luminol test—reaction with blood to produce light
Luminol is the most sensitive chemical test that is capable of presumptively detecting bloodstains diluted up to 300,000 times. Its reaction with blood emits light and thus requires the result to be observed in a darkened area.
Precipitin test—blood is injected into a rabbit; antibodies are formed; the rabbit’s 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.
Larger nucleic red blood cells
Red blood cells are most numerous; 5 to 6 million per mm3
White blood cells are larger and less numerous; 5,000 to 10,000 per mm3
Platelets are tiny, cellular fragments; 350,000 to 500,000 per mm3
The average adult carries 4 to 5 L of blood.
42% 12% 3% 43%
of the population in the United States
(of which 85% is Rh+)
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.
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 type B blood.
Blood type O has neither antigen A nor B and will not agglutinate.
A nor B
A, B, O, AB
A and B
A nor B
A, B, O, AB
A and B
BTW: When packaging and storing blood evidence, do not block out air (no sealed containers). Use a paper bag or envelope.
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.
Antibodies are proteins secreted by white blood cells that attach to antigens to destroy them.
Antigens are foreign molecules or cells that react to antibodies.
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.
Serology involves a broad scope of lab tests that use specific antigen and serum antibody reactions.
An antibody reacts or agglutinates only with its specific antigen. The concept of specific antigen-antibody reactions has been applied to techniques for detecting drugs in blood and urine.
Every red blood cell contains either an A antigen, a B antigen, or no antigen (this is called type O). The type of antigen on one’s red blood cells determines one’s ABO blood type.
The determination of blood is best made with a preliminary color test. Review the presumptive tests.
The gene is the basic unit of heredity. A chromosome is a threadlike structure in the cell nucleus, along which the genes are located.
Most human cells contain 46 chromosomes (23 mated pairs). Egg and sperm contain 23 unmated chromosomes.
An allele is any of several alternative forms of genes that influence a given characteristic and that are aligned with one another on a chromosome pair.
A heterozygous gene pair is made up of two different alleles. A homozygous gene pair is made up of two similar alleles.
When two different genes are inherited, the characteristic coded for by a dominant gene is expressed. The characteristic coded for by a recessive gene remains hidden.
A genotype is the particular combination of genes present in the cells of an individual. A phenotype is the physical manifestation of a genetic trait.
Type A blood (phenotype) can be AA (homozygous genotype) or AO (heterozygous genotype). Type B blood can be BB or BO. Type AB blood is only AB genotype. Type O blood is only OO genotype.
Review how to do Punnett squares with blood types to determine parent/offspring relationships.
80% of the population are secretors. Their blood-type antigens are found in high concentration in their body fluids such as saliva, semen, vaginal secretions and gastric juice.
Scene Pattern Reconstruction
1. Stain condition
Lab Results Reconstruction
1. Genetic marker typing
2. Age determination
3. Source determination
4. Race determination
5. Sex determination
—From Cracking Cases by Dr. Henry C. Lee and Thomas W. O’Neil
A field of forensic investigation that deals with the physical properties of blood and the patterns produced under different conditions as a result of various forces being applied to the blood.
Blood, as a fluid, follows the laws of physics.
Paul Kirk (1902–1970) was a professor of criminalistics and biochemistry at the University of California at Berkeley. He actively assisted law enforcement organizations from 1935 to 1967. His book Crime Investigation contained a chapter in which he discussed the application of bloodstain pattern analysis to criminal investigations. Dr. Kirk analyzed the bloodstain pattern photos from the Sam Sheppard case and was instrumental in Sheppard’s release after his second trial. Find out more about the case at truTV’s Crime Library.
A blood droplet remains spherical in space until it collides with a surface.
Once a blood droplet impacts a surface, a bloodstain is formed.
Droplets falling from the same height, hitting the same surface at the same angle, will produce stains with the same basic shape.
How will the shape change as the height is increased or decreased?
A droplet contains approximately 0.05 cc of fluid.
Is not the same for all blood droplets, but is generally from 0.03 cc to 0.15 cc
Is directly dependent upon the surface or orifice from which it originates
The impact area is called the target.
Size of the droplet
Angle of impact
Velocity at which the blood droplet left its origin
Texture of the target surface
On clean glass or plastic—droplet will have smooth outside edges
On a rough surface—will produce scalloping on the edges
The distance between the target surface and the origin of the blood
The point(s) of origin of the blood
Movement and direction of a person or an object
The number of blows, shots, etc., causing the bloodshed and/or the dispersal of blood
Type and direction of impact that produced the bloodshed
The position of the victim and/or object during bloodshed
Movement of the victim and/or object after bloodshed
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.
Angle of impact—angle at which blood strikes a target surface
Bloodstain transfer—when a bloody object comes into contact with a surface and leaves a patterned blood image on the surface
Backspatter—blood that is directed back toward the source of
Cast-off—blood that is thrown from an object in motion
Contact stain—bloodstains caused by contact between a wet blood-bearing surface and a second surface that may or may not have blood on it
with a particular object
have blood on it
bloodstain, altering the appearance of the original stain
Describe each of these:
a. passive drops
b. arterial gushes
Directionality—relates to the direction a drop of blood travels in space from its point of origin
Terminal velocity—the greatest speed to which a free-falling drop of blood can accelerate in air. It is dependent upon the acceleration of gravity and the friction of the air against the blood—approximately 25.1 feet/second.
The shape of a blood drop:
Round—if it falls straight down at a 90-degree angle
Elliptical—blood droplets elongate as the angle decreases from 90 to 0 degrees; the angle can be determined by the following formula:
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?
The more acute the angle of impact, the more elongated the stain.
90-degree angles are perfectly round drops; 80-degree angles take on a more elliptical shape.
At about 30 degrees the stain will begin to produce a tail.
The more acute the angle, the easier it is to determine the direction of travel.
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?
The harder and less porous the surface, the less the blood drop will break apart.
The softer and more porous the surface, the more the blood drop will break apart.
The pointed end of the bloodstain faces the direction of travel.
The location of the blood source can be determined by drawing lines from the various blood droplets to the point where they intersect.
The area of convergence is the point of origin—the spot where the “blow” occurred. It may be established at the scene by measurement of angles with the use of strings.
Lines of convergence
Draw straight lines down the axis of the blood spatters.
Where the lines converge, the blood originated.
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.
Class evidence for blood includes blood type. If you can determine the DNA, you will have individual evidence.
Bloodstain patterns are considered circumstantial evidence in a courtroom. Experts can argue many points, including direction of travel, height of the perpetrator, position of the victim, left/right hand, whether the body was moved, etc.
Herbert L. MacDonell is considered by many to be the father of modern bloodstain pattern analysis. He is the director of the Lab of Forensic Science and founder of the Bloodstain Evidence Institute (1973) in Corning, NY. His book Bloodstain Pattern Interpretation helped to jump-start this discipline. He has consulted on criminal cases in all 50 states, in addition to testifying in the O. J. Simpson trial and in the assassination cases of Sen. Robert F. Kennedy and Dr. Martin Luther King, Jr.
For additional information about blood evidence, and famous crimes that involve serology, check out truTV’s Crime Library at: