Blood typing evidence is now used more to exclude a suspect than to identify a suspect
Answers
In the past what was being done in a crime scene was to take blood samples from the scene and the determine its group this is to say that typing is done after which the suspects will also go through the process of determination of their blood groups and when their blood group matches the one obtained from the crime scene, they may face the prosecution and if it does not match the suspect is excluded from the case.
But recently what is being done is to determine the fingure prints obtained from the crime scene. This is the most accurate way of determining the real suspect since fingure prints differ from person to person.
Initially what was done was blood samples were collected from a particular crime scene and then blood typing was done.
Now, after doing the blood typing of the suspect if the blood samples matched, the suspect was considered for further interrogation and if the samples did not match they were excluded.
But nowadays, better forms of investigation like finger printing, DNA printing techniques are used which are more accurate methods of investigation.