How do your blood cells become bodies of evidence in forensic science? How does it help the criminal files? In instances of a brutal homicide, there are adequate traces of blood on the victim, his surroundings, and discarded weapons. The offender possibly carries blood in his clothes as well. When you match the blood, it invokes a line of possibility that you have landed on the criminal.
1) Is the stain actually blood?
A red blotch of stain can be tested using the Kastle-Meyer test to identity if it is actually blood. This test rests upon the presence of peroxidase in human blood. The stain is extracted with a damp filter paper and treated with a mixture of phenolphthalein and hydrogen peroxide. From a pink coloration, we can infer that it is blood. It is further tested to know if it is human or animal blood.
2) Does the blood belong to a male or a female?
The male and female body cells can be differentiated in that the nuclei of the female cells have a body called the ‘Barr body’. This is absent in male cells.
3) What is the Blood group?
It was only in the 19th century that Austrian physiologist Karl Landsteiner brought a solution to the constant failures in blood transfusion procedures. He was the one to tell people that there are four varieties of blood in humans and that blood tranfusions are only possible between matching groups. The red blood cells carry substances called antigens which produce antibodies to fight against any infections or diseases that we may contract. This physiologist classified blood into four groups depending on the presence and absence of two specific antigens.
* When antigen A is present and antigen B is absent, then person belongs to Blood Group A.
* When antigen A is absent and antigen B is present, the person is Group B
* When the red blood cell has both the antigens A and B, it belongs to Group AB
* When the person neither has A nor B antigens, he is Group O.
4) Tracing the criminal
If the person belongs to Blood type O and there are also 47% of the population who belong to the O type. But the substance haptoglobin-2 occurs in 36% of person who have O type and the enzyme PGM-2 occurs in 5% of these. This narrows down to just 8 people in a population of 1000 who have this type of O Blood Group. This takes us very close to the criminal.
5) What else if not blood?
About 80% of humans are “secretors” which means that their bodily fluids such as saliva, sweat, urine and semen contain the same substances as their blood. So, if the person has been killing by choking or drowning, there can be no blood loss involved. In such circumstance, this can home handy.
However the simple ABO blood test can help eliminate many from the list of suspects and help us identify the perpetrator.