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Chapter 7: Blood and Blood Spatter

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Presentation on theme: "Chapter 7: Blood and Blood Spatter"— Presentation transcript:

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


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