Biology- DNA, etc.?

DNA fingerprinting should be used to identify if the blood found under the victims fingernails are from the blood in the scratches of the 2 ppl at the scene. this is so that we can know if they are the ailants of the victim. The piece of torn clothing with blood stain shoud also be tested for DNA because we can then know if the blood came from the victim, the 2 ppl at the scene or other ppl, who had escaped. We should find out if the 2 ppl at the crime scene were indeed innocent or if they were the robbers. we should also establish if the 2 ppl were really unrelated, through DNA tests.