Blood stores in itself a variety of information that could be generated by Forensic Science Laboratories and could be interpreted by the investigating officer for the benefit of the investigation.
(A) Whether the questioned stain is blood or not?
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As rightly said, everything that glitters is not gold. Similarly, every red stain found at the crime scene is not blood. In many cases, a lot of energy and time could be saved by answering this question as some red stains mistaken as bloodstains can mislead the investigation. So every stain must be tested for being blood or not. Further examinations are based on the result of the answer to this question.
(B) Is blood human? If yes, what is the blood group?
After establishing the presence of blood, the next step is to ascertain that it is human blood and to verify the blood group.
Blood Grouping: There is a variety of systems for determining the blood groups for distinguishing individuals. The most commonly used method is ABO system. Other significant systems are Rh and MNS. If needed, other policies based on protein and enzymes present in the blood can also be followed. Above all, DNA fingerprinting can be done to serve the purpose. There are 256 antigens and about 25 blood group systems based on association with these antigens.
Blood grouping can also help in establishing the paternity/maternity of a child in some cases. It cannot be said that someone is the father or mother of a child, but it can be said that a particular person or woman could not be the child’s parent.
If the blood is not human, then of which animal species thereof? An investigation officer should know that the FSL could answer this question. Almost every animal is red and cannot be distinguished from human blood by visual examination. So criminals take benefit of this fact and sometimes spill over some animal’s blood at the scene of the crime and try to indicate what is not valid. This is done by them to implicate/harass others or confuse the police and mislead the investigation line.
If blood is human, whether of male or female origin?
This question is also sometimes helpful in providing definite direction to the investigation. If it could be known that the source of blood in question is male or female, then, in either case, the investigation officer will look for the source in the suspects of that particular sex group only, thereby saving time and energy.
Males and females have different types of sex chromosomes, and sex of the source of blood can be determined from the presence of a particular kind of sex chromatins. Menstrual blood exclusive for females can be distinguished from other samples.
From which part of the body, the blood has originated?
It is usually tough to tell the exact part of blood origin, but extraneous material present in the blood can indicate the possible place of birth.
Menstrual blood: Usually found on undergarments, diapers, or pieces of cloth. The presence of endometrial and vaginal epithelial cells indicates its place of origin.
Blood from the nose: Blood from the nose may contain nasal mucus and hair from the nose.
In case of blood due to rape, the presence of semen and pubic hair may be of great assistance.
Whether alcohol/poison is present or not? Analysis can tell whether the blood contains alcohol or poison in it. If yes, then it’s the quantity type and whether it exceeds the lethal limit of that particular substance (alcohol/poison).
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