Why is blood collected at crime scenes?
There's still white blood cells with DNA.

Some forensic blood tests are:

Conventional serological analysis:


Analysis of the proteins, enzymes, and antigens present in the blood, for general doctor tests: (black/white/drunk/stoned/heroin addict/polio vaccinated/hiv pos...)


Restriction Fragment Length Polymorphism (RFLP) DNA :


Direct analysis of certain DNA sequences present in the white blood cells. This method also usually requires a "large" sample size to obtain significant results.


Polymerase Chain Reaction (PCR) DNA :


Analysis of certain DNA sequences that have been copied multiple times to a detectable level.