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BLOOD

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Introduction and History Introduction and History

Blood typing can provide class evidence Using DNA from blood is individual

evidence Blood spatter patterns provide information

about the origin of the blood, the angle and velocity of impact, and type of weapon used

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Composition of Blood Composition of Blood

Whole blood carries cells and plasma—the fluid with hormones, clotting factors, and nutrients.

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.

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Blood Typing—Proteins

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.

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Blood Typing—Antibodies; Additional

Proteins and Enzymes

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.

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Blood Typing—Probability and Blood Types

By identifying the additional proteins in the blood evidence sample, investigators can limit the size of a suspect population and help identify a suspect.

For example: What is the chance of throwing dice and getting two sixes?

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BR

What are the four blood types and their percentages in the population?

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Science of Murder clip

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Use of luminol to find blood stainsthat are no longer visible to thenaked eye.

Luminol reacts with hemoglobin toproduce a blue glow. The brighter and stronger the glow, the fresherthe blood.

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Blood SpatterBlood Spatter

In 1955, blood spatter analysis was first used in a courtroom to free Sam Sheppard (The Fugitive).

When a wound is inflicted, a blood spatter pattern may be created.

A grouping of blood stains is a blood spatter pattern.

The pattern can help to reconstruct the events surrounding a shooting, stabbing, or beating.

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Blood Spatter Analysis

Analysis of a spatter 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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The next slide contains a strong image.

Feel free to turn you head

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OJ Simpson crime scene

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Blood Spatter

Blood is a mixture of blood cells and plasma

It is cohesive – meaning it sticks together

Maintains a circular shape

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Blood Drop Characteristics

Although blood drops remain circular, they can have satellites or spikes

Parts of the blood that separate from the main drop are called satellites

Spikes remain attached to the large drop

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QuickTime™ and a decompressor

are needed to see this picture.

satellite

spikes

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Blood dropped from different heights

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Blood Spatter Analysis—Six Patterns

Describe each of these: a. passive drops b. arterial gushes c. splashes d. smears e. trails f. pools

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Blood Spatter Analysis—Impact

Patterns can help investigators determine the type of weapon used.The faster the blow, the smaller the

drops

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Types of Injury

High velocity

(gunshot)

Medium velocity

(hammer strike)

Low velocity ( drip)

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Blood Spatter 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?

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Determining direction of travel

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Wave Cast-offWave Cast-off

.Parent drop

wave cast-off

Tail of wave cast-off points back to parent drop

Tail of elongated stain points in direction of travel

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http://projects.nfstc.org/gallery/main.php?g2_itemId=3857

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Dexter movie clip

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Location of the Origin of the Blood

Lines of convergence Draw straight lines down the axis of the

blood spatters. Where the lines converge, the blood

originated.

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Lines of Convergence Draw line through the axis of the main droplet

Start at the end of the blood drop and draw toward the source

Do not draw lines through satellite drops

Draw smallest circle around intersection -marks point of convergence

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Points of Convergence

The red circle shoes the point of convergence.

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Point of ConvergencePoint of Convergence

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Angle of ImpactAngle of Impact

length

width

Angle of impact = arc sin W/L

Distance from point of convergence

Hei

ght a

bove

poi

nt o

f co

nver

genc

e

Origin

85 60 45 30

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Angle of Impact

Take the inverse sin of width/length

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Determine Angle of Impact

Width Length sine arc sine

2 3 .6667 42°

1 4 .25

9.6 9.7

14.5°

.9897 82.2°

Hand-out

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The point where the lines of spatter connect

is called the point of convergence. This

shows where the blood came from, which is where the victim was

at the time of the attack.

In the diagram to the right, strings were used to

determine the point of convergence. Wherever the strings connect is where the spatter came from (where

the victim was).

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Crime Scene Investigation Crime Scene Investigation of Bloodof 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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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SummarySummary

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

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

Blood spatter evidence can be used to recreate a crime scene.

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