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.
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
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.
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
b. your RBC’s can be covered with 1 of these antigens, bothof these antigens, or neither of these antigens.
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5. Rhesus (monkey) Factoralso called the D Factor
a. The Rh blood system, people are either Rh + or Rh –
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)
C. Spatter Pattern depends 1. On the amount of blood
a.mist –tiny droplets<1mm diameter
tremendous forces,gunshot at close range
b. until the blood drop reaches terminal velocity at 48” distance, diameter remains constant.
3” 6” 12” 24”48” 56”
1.The velocity of a free falling drop of
blood is limited to the force of gravity called Terminal Velocity =
25 ft/sec
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
e. path of the blood drops -if several feet apart with tails= indicates someone was bleeding and also running.
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
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
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
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
1. the appearance w ill depend on:
a.)Amount of blood pooled near a bloody object or from the victim.
2. after the blood dries, the majority of the liquid portion (55%) of blood will evaporate leaving the cellular (solids) part(45%) behind.