Blood EvidenceI. Identifying Blood Evidence

A. Presumptive Tests –a test to determine if a stain is blood

Ex. Stain- _________________Pattern -_________________

a. Kastle-Meyer Test:

1. use of color indicator to identify a stain as blood.

2. hemoglobin= the red pigment/protein in blood.

3.peroxidase-like reactionan enzyme reaction with

peroxide

4.and color reaction with phenolphthalein turns

pink.

Steps: Kastle-Meyer Test

1.) Drop of water on q-tip rub on stain2.) add 1 drop of Kastle-Meyer Reagent 3.) 1-2 drops Peroxide

Then (phenolphthalein =pink color change)

5.False-Positives: some vegetable materials turn PINK like blood that are not blood .-potatoes

-horseradish

b. Luminol Test: (large stains or spatter patterns)

1.it is a reaction to create LIGHT called Luminescences.

2. Suspect stain areas are sprayed with Luminol and viewed in the dark.

3. The ironcomponent in the hemoglobin molecule reacts with the Luminol to create the Luminescence.

FF The house that roared

II.What is blood?Copy into your notes :ActivationWhat do you notice about this blood stain?Can you explain why it looks this way?

A. What is blood?1. Blood is a complicated mixture of different kinds of cells, dissolved in a liquid substance.

2. Two phases of blooda. Solids – cells

1.) Red blood cells- erythrocytes2.) white blood cells-

leukocytes3.) platelets - thrombocytes

Blood solids

b. Liquid – plasma(serum)55% of blood90% WATER

3. Exsanguination-To bleed to death from continuous blood loss

4. How much blood do we have in our body?

a. A unit = 500mlb. An adult human =5 - 6

liters of blood.c. average adult =will have

10-12 units of blood.

B. ABO/Rh blood typing

1.Blood evidence is often used to associate a suspect with a crime or scene.

2. Serology is the study of blood chemistry.

3. Serology: important factors or types.

a.A,B, and O factors

b.Rhesus Factor (Rh)

a. Letters A and B represent 2 different types of antigens, or molecules, that can be found on the surfaces of the red blood cells.

4. The ABO Blood System

Blood Type Antigen on RBC

Blood Cells with Antigen

A

B

AB

O NONE

anti-A

anti-B

Anti-A and B

b. your RBC’s can be covered with 1 of these antigens, bothof these antigens, or neither of these antigens.

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c. therefore there are 4 blood types in the system.

A, B, AB or O

d. Agglutination-the RBC antigens are clumping due to the action of antibodies.

5. Rhesus (monkey) Factoralso called the D Factor

a. The Rh blood system, people are either Rh + or Rh –

6. In the past, blood factorswere used to identify victims and suspects.

7. Since 1985, Blood type was replaced with DNA typing .

8. Percentage of PeopleBlood Types

type of blood % of people with this type

O 43A 42B 12

AB 3

Rh Factors

Rh typeanti-serum

% of populat

-ion

+ Rh+(clumps) 85%

- Rh- (no clumps) 15%

9. Universal Donor 0Universal Acceptor AB

10. Agglutination-the RBC antigens are clumping due to the action of antibodies.

III. Blood Drop Behavior (Spatter)A. The spatter pattern is dependent on the following:

1.amount of blood in the drops

2.angle in which it impacts a surface

3.velocity of the blood drop4.forces applied to the drops5. The distance the blood traveled

6. the impact surface texture

B. Blood drop behavior in the air once it has left the body:1. depends on how it left the body ( gunshot, blunt force, or sharp instrument)

2. Once the drop of blood impacts a surface, the spatter pattern or the blood stain is created.

C. Spatter Pattern depends 1. On the amount of blood

a.mist –tiny droplets<1mm diameter

tremendous forces,gunshot at close range

b. fine droplets <3mm in diameterdue to forces greater than gravity (blunt force trauma)

c. mediumdroplets3-6 mm in diameterdue to gravity and forces (beating)

d. largedroplets

>6 mm in diameter

due to gravity alone

2. the angle at which blood impacts

Flat surface

90oangle

Flat surface

45oangle

Flat surface

10oangle

Rule:the smaller the angle, the more elliptical the drop

shape

3. Distance blood dropped-

a.the greater the distance the larger the spatter diameter

b. until the blood drop reaches terminal velocity at 48” distance, diameter remains constant.

3” 6” 12” 24”48” 56”

c. at greater distances, the droplet becomes “crenellated”-smaller droplets (satellites break free)

D. velocity(speed)

1.The velocity of a free falling drop of

blood is limited to the force of gravity called Terminal Velocity =

25 ft/sec

Low velocitychanges to

medium velocity>25 ft/s

2.Medium velocity impact blood spatter

a. Produced by external, medium velocity forces.

b. a force caused the blood to move from the direction of its source.

Newton’s 2nd LawF= m x a

medium velocitychanges to

high velocity>100 ft/s

E. Blood Spatter Patterns (BSP)

Dr.Henry Lee at O.J. Simpson’s house .

1. Passive Blood Stainsa.Drip pattern-created when

blood drips into blood

b. blood drop trails-

1.)How? the blood dripped from a bloody source onto a surface.

2.)Trails froma body being dragged or

carried

c. blood trails , depend on

1.) how fast the person was moving or dragged

2.) the volume of blood they are casting off

d. Directionality- blood stains will have “tails” with the drop. The tail points in the direction in which the drop was moving.

Tail

Directionality

Blood falls right to left

The source of the blood was moving left To right!

e. path of the blood drops -if several feet apart with tails= indicates someone was bleeding and also running.

1.) if drops are closer together and more rounded= person walkingor staggering.

f. Flow pattern- a change in the shape and direction of a bloodstain due to the influence of gravity or movement of an object

2.Void Patternis an empty space where blood should have been.

What would create a void pattern?

3. Transfer Bloodstainsa. Pattern/ Contact

transfer- created when a wet, bloody surface comes in contact with a second surface

b. Wipes-created when an object moves through an

existing stain, removing and altering its appearance

c. Swipes-the transfer of blood from a moving source onto a unstained surface.

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d. hair swipe-hair movement with blood creates a unique pattern.

e. Smear- suggests that the object pressed against the surface will also be stained.

4. Impact or projected

bloodstainsa. Spatters –Impact patternsproduced by forces greater than gravity

1.) Forward-blood which travels in the same direction of a bloodstain due to the influence of gravity or movement of the object.

2.) Back-blood directed back towards the source of the energy or force that caused the spatter

2

3.) Blow-Back spatter-

“Draw-back effect”- blood in the barrel of a firearm that has been drawn backward into the muzzle

- On the hand of the shooter

b. Cast-off pattern-

created when blood is released or thrown from a blood bearing object in motion

1.) Expirated blood pattern -blood that is blown out of the nose, mouth, and or wound as a result of high air pressure

2.) Spurts- blood from a major artery, called an arterial spurt.

3.). Splashes, from blood flying through the air and hitting a surface at an angle

4.) Other: Skeletonized stains- as blood dries, the edges dry first due to surface effects. If the blood is wiped the edges remain behind.

c. Determining the origin of the spatter =Point of Convergencecalled “pulling strings”

Dr. Dexter Morgan

d. Pooled Blood (cast-off & passive)

1. the appearance w ill depend on:

a.)Amount of blood pooled near a bloody object or from the victim.

b.) the time it takes for the blood to coagulate-solid and liquid parts of blood separate

2. after the blood dries, the majority of the liquid portion (55%) of blood will evaporate leaving the cellular (solids) part(45%) behind.

Pilar MacCarther’s Death:blood smear was made by clear serum.

Dr. Lee: “It takes more than15-20 minutes for the 1000ml of blood to coagulate.”

Pool