Blood Identification Tests

Test 1: Identify which is blood using hydrogen peroxide

Sample	Prediction and reason for prediction before test	Observation (during the test)	Result
1	May contain blood as it is red in colour and has a high viscosity.	No bubbles	Negative
2	Not blood. Orange in colour.	No bubbles	Negative
3	Not blood. Bright pink in colour and very low viscosity.	No bubbles	Negative
4	May contain blood as it looks red and fairly thick.	Bubbles observed	Positive
5	Not blood. Bright purple in colour.	Bubbles observed	Positive
6	Probably not, but may be blood.  Red in colour, looks like chilli with many small particles floating around	Bubbles observed	Positive

Samples tested positive for catalase: Samples 4,5,6

Test 2: Identify which is blood using Luminol

Sample	Observation	Result
1	-	-
2	-	-
3	-	-
4	Glowed	Positive
5	Glowed	Positive
6	Glowed	Negative

Samples tested positive: Samples 4,5

Test 3: Kastle-Meyer Reagent

Sample 4 turned pink whereas Sample 5 did not change colour at all.  Hence, my conclusion is that Sample 4 is blood.

Questions:
1. Why is it necessary to use more than one test to determine whether the given stain is blood?
More than one types of substances can give the same positive results.  For example,

• Luminol chemiluminescence can also be triggered by a number of substances such as copper or copper-containing alloys, and certain bleaches; and, as a result, if a crime scene is thoroughly cleaned with a bleach solution or horseradish, residual cleaner will cause the entire crime scene to produce the typical blue glow, effectively camouflaging any organic evidence, such as blood.
• Luminol will also detect the small amounts of blood present in urine, and it can be distorted if animal blood is present in the room that is being tested.
• Luminol reacts with fecal matter, causing the same glow as if it were blood.
• Luminol's presence may prevent other tests from being performed on a piece of evidence. However, it has been shown that DNA can be successfully extracted from samples treated with luminol reagent.

Hence, it is essential to use a series of tests to confirm that the given stain is really blood and not any other substance.

2. Once you know that a stain is real blood, what else would you do as a forensic scientist?
I would isolate the DNA in the blood to find out who it belongs to.  If it belongs to anyone other than the victim, I can interrogate the person to find out if he or she was involved in the murder.