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Chapter 8 Blood and Blood Splatter By the end of this chapter you will be able to:

o Explain the composition of blood o Describe the function of blood cells o Determine the blood type of a blood sample o Conduct a blood splatter analysis o Examine wounds and describe the nature of the

weapon o Find and process blood evidence

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Introduction and History Introduction and History

o Blood typing provides class evidence o DNA profiling provides individual evidence o A blood splatter pattern provides information

• the truthfulness of an account by a witness or a suspect

• the origin of the blood• the angle and velocity of impact • the type of weapon used

Blood History – studied for thousands of years!

Date Who Contribution

1628 Sir William Harvey Noted continuous circulation within the body

1874 Sir William Osler Discovered platelets

1901 Karl Landsteiner Discovered types: A, B, O

1940 Karl Landsteiner Discovered Rh protein

1959 Dr. Max Perutz Described structure of hemoglobin

1971 Dr. Blumberg Developed method of antibody detection

1987-2002 Various Blood screening tests for infectious diseases

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Composition of Blood Composition of Blood

Blood is a circulating tissue consisting of:

o Red blood cells (Erthrocytes)—carries oxygen to the body’s cells and carbon dioxide away

o White blood cells (Leukocytes)—fights disease and foreign invaders and, alone, contain cell nuclei

o Platelets (Thrombocytes)-aids in blood clotting and the repair of damaged blood vessels

o Plasma—a liquid suspending other blood components

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Composition of Blood Composition of Blood

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Cellular Components of Blood

• The immune system functions to protect our bodies by identifying cells or molecules that are foreign, such as viruses, bacteria, and other parasites.• White blood cells secrete proteins, antibodies that assist in the immune response.

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Blood Typing—Proteins

o 1982 white blood cells were used as a source of DNA by Dr. Alec Jeffreys to produce the first DNA profile

o Discovered in 1900 by Karl Landsteiner – blood cannot be freely mixed with anothers blood

o Identifies the presence or absence of particular proteins embedded in the cell

o Quicker and less expensive than DNA profilingo Produces class evidence but can still link a

suspect to a crime scene or exclude a suspect

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Blood Enzymes

o Enzymes are complex proteins that catalyze different biochemical reactions

o Many enzymes and proteins have been found in the blood that are important for identification purposes

o The more enzymes available for testing, the easier it will be to identify a person.Examples: Phosphoglucomutase (PGM) Adenylate kinase (AK) Adenosine deaminase (ADA) Esterase D (EsD) Glucose-6-phosphate dehydrogenase (G-6-PD) Haptoglobins (Hp)

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Blood Typing—Antibodies

o Antibodies are Y-shapedproteins secreted by whiteblood cells that attach toantigens to destroy them

o Antigens are foreign molecules or cells that react to antibodies

Ex. Viruses, bacteria, red blood cells from another person

**There are more than 300 know blood group proteins and more than 1 million different protein binding sites on each red blood cell.

Agglutination – clumping occurs when one arm of the Y shaped antibody attaches to the red blood cell, the second arm attaches to another red blood cell.

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Blood Typing—Proteins

42% 12% 3% 43%of the population in the United States

• If a person contains only protein A = A blood• If a person contains only protein B = B blood type• If the person’s blood has both the A and the B proteins, then he or she has type AB blood.

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Rh Factor

85% of the population has a protein calledRH factor on their blood cells

People with Rh+ can get Rh+ and Rh- Rh- can only get Rh-

Blood Typing

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Blood Typing

Blood typing!

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Blood Typing

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The Blood Typing Game

Blood Typing

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Antibodies fight antibodies

Donor Receiver

0 0

A A

B B

AB AB

Blood group AA antigens on the surface of your red blood cells and B antibodies in your blood plasma.

Blood group BB antigens on the surface of your red blood cells and A antibodies in your blood plasma.

Blood group ABA and B antigens on the surface of your red blood cells and no A or B antibodies at all in your blood plasma.

Blood group 0neither A or B antigens on the surface of your red blood cells, have both A and B antibodies in your blood plasma.

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Blood Typing—Probability and Blood Types

o The probability of a blood type equals the product of probabilities for each protein group

If Type A = 42% and Rh Factor = 85%

Then A+ = .42 x .85 = .357 (35.7%)o Knowing additional proteins and enzymes in the

blood sample • Narrows the population group • Increases the probability of identifying a suspect

A 42%B 12%AB 3%O 43%

MM 30%MN 48%NN 22%

Rh+ 85%Rh- 15%

Hp-1 14%PGM-2 6%

Probabilities

o What percentage of the population has A+

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.42 X .85 = .357 35.7% Therefore about 36 out of every 100 people

o What percentage has O- ,MN.43 X .15 X .48 = .031 3.1% of the population!

o What percentage has A,NN,Hp-1,Rh-,PGM-2 .42 X .22 X .14 X .15 X .06 = .000116 .0116 % of the population

Again, by testing for more blood-type proteins, the probability for uniqueness continues to increase, and the number of other people with the same combination as our suspect decreases.

Blood Spatter

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Blood Splatter

o 1939—splatter patterns first analyzed

o Today, blood spatter evidence is used to explain events at a violent scene

o Blood may splatter when a wound is inflictedo Blood splatter pattern—a grouping of blood stainso Patterns help to reconstruct the events

surrounding a shooting, stabbing, or beating

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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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Blood Splatter Analysis

Natural cohesiveness of blood

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Blood Splatter Analysis

o Satellite droplets—• When blood falls from a height, or at a high velocity,• It overcomes its natural cohesiveness, and

separates from the main droplet

o Spiking patterns—• Form around the droplet

edges when blood falls onto a less-than-smooth surface

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Blood Splatter Analysis—Six Patterns

Describe each of these: a) Passive drops - dropped at 90 degrees b) Arterial gushes - walls or ceilings cause by

pumping c) Splashes - exclamation pointd) Smears – bleeding victim leaving blood as they

brush against something Ex. walle) Trails - bleeding victim moving locationsf) Pools – bleeding heavily and remaining in one

place

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Round – dropped at 900

Tails or satellites – determine directionbbSpatter – type of pattern

>3mm Low velocity 1-3mm Medium Velocity <1mm High Velocity

fine mist – high velocity impact EX. GunshotCast off –lower velocity EX. Hit with batVoids – person was moved

Blood Descriptions

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Blood Splatter Analysis—Impact

Patterns can help investigators determine the type of weapon used

o What kind of a pattern is produced by a gun shot?

o What kind of a pattern is produced by a hammer blow?

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Blood Splatter Analysis—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?

Adhesion – force between two unlike surfacesSurface tension -elastic characteristic along the outer edge of a liquid caused by the attraction of like molecules

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Blood Splatter Analysis

Lines of convergence—two or more blood splatters can pinpoint the location of the blood source

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Crime Scene Investigation of Blood

1. Search for blood evidence 2. Determine

a. Is the evidence blood?b. Is the blood human?c. What is the blood type?

3. Interpret the findings: a. Does the blood type match a suspect’s blood?b. If not, exclude that suspectc. If yes, decide if DNA profiling is necessary

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. . . . . . . . . . . . . . . . . Summary

o Blood consists of cellular components and plasma. o The various human blood types are caused by the

presence or absence of A and/or B proteins on the surface of red blood cells.

o Blood splatter evidence can be used to recreate a crime scene.

o Investigators endeavor to (a) locate, (b) identify, and (c) interpret blood splatter patterns at crime scenes.