To find out which, rely on the other evidence. You would not expect to find blood at the scene unless there were a confrontation. Gathering your evidence is extremely important. Even things that appear totally redundant may actually be very important. Since the scene is like a puzzle, you can begin putting it into perspective using the evidence in as much as a sequential order as possible.
Many items are available for examination.
For example, fingerprints, hand prints, shoe and tire impressions, tools and toolmarks, weapons and ammunition, glass, soil, hair and fibers, body fluids, documents, safe insulation, rope and tape, drugs, and explosives. Since the evidence will be used throughout the entire investigation and court trials, it is very important to avoid common errors. First, not taking enough of the sample evidence, also, not obtaining standards of comparisons, and finally, not keeping the evidence's integrity in tact. Proper collection, documentation, and chain of custody are your best friends. A standard comparison is an object, measure, or model with which evidence is compared to determine whether both came from the same source.