The method used to collect fingerprints can differ depending on the surface. Regular powder is used to collect fingerprints off glass and painted surfaces, while magnetic powder is used on shiny...
If you are speaking of during the initial investigation and apprehension - for an identification of the apprehended suspect. Because that's usually where the victim and any witnesses will be.
The DNA of each individual is unique. No two individuals share the same genetic make up unless they are identical twins. Analyzing DNA samples found at a crime scene can help place a suspect at the...