1. Chapter 7: Blood and Blood Spatter
Part 3: Crime Scene Investigation of Blood

2. Crime Scene Investigation of Blood
Questions for a Criminalist
Is it blood?
Is it human blood?
If it is human, can it be linked to a suspect/victim and how closely

3. Crime Scene Investigation of Blood
Test to Identify if the Blood is Human
Kastle-Meyer Test: mixes blood, phenolphthalein and hydrogen peroxide
Hemoglobin (Iron) in the blood causes the phenolphthalein to turn bright pink
Test is presumptive or preliminary test for blood
Substances other than blood may produce false positive results

4. Crime Scene Investigation of Blood
Test to Identify if the Blood is Human
Luminol: chemical that exhibits chemiluminescence
Striking blue glow when mixed with an appropriate oxidizing agent
a solution of hydrogen peroxide, hydroxide in water is used as the activator
Glows bright blue in the dark when it comes in contact with blood

5. Crime Scene Investigation of Blood
Test to Identify if the Blood is Human
Luminol Continued
Advantages of Luminol
Allows you to detect stains that would not be ordinarily visible
Can be used in very dilute concentrations
Allows criminalist to spray large areas
Does not interfere with DNA
Allows criminalist to collect DNA samples for DNA analysis after it was sprayed with luminol

6. Crime Scene Investigation of Blood
Test to Confirm the Blood is Human
ELISA Test (Enzyme Linked Immunosorbent Assay)
Human blood is injected into rabbits
Rabbits produce antibodies against human blood
Antibodies are isolated from the rabbit blood and stored
When a sample of human blood is mixed with the antibodies it will cause coagulation (blood clumping)
Coagulation confirms the presence of human blood

7. Crime Scene Investigation of Blood
Test to Confirm the Blood is Human
Gel Diffusion Test
Antigen (from the human blood sample) and antibodies (from the rabbit blood samples) are placed in separate wells in a gel
Samples are forced to move towards each other
If they bind to each other, they form a single line of precipitate in between the wells
This is a positive test for human blood

8. Crime Scene Investigation of Blood
Test to Confirm the Blood is Human
DNA Test
DNA testing is the ultimate test

9. Check for understanding 1
3 things a criminalist must find out
Test which causes phenolphthalein to turn bright pink
3 advantages to using luminol
Ultimate test for human blood
Human blood is injected into rabbits causing rabbits to build antibodies to the human blood
Glows bright blue in the dark when it comes in contact with blood
Samples bind to each other forming a precipitate line
intersection of lines formed by drawing a line through the main axis of at least two drops of blood drops of blood that indicates the general area of the source of the blood spatter