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Every crime scene is different. Yet, our primary job as crime scene investigators is always the same: to tie a suspect to the scene. The way to accomplish this goal is to collect as much evidence as possible from the scene and the suspect.
No matter what type of crime scene you encounter, you must be thorough when processing it. In most cases, you’ll begin by looking for fingerprint, DNA, and impression evidence. Process everything that a suspect may have come into contact with. Don’t forget less obvious things like a piece of paper, a car steering wheel, a hat, or a cigarette butt. Make sure you check AFIS for a fingerprint match and CODIS for a DNA. When working with impression evidence, be sure to photograph everything before taking the impressions. That way, you’ll have a record of the evidence if your impressions get damaged during processing. Once you have a suspect, match his fingerprints, DNA, and impressions to what you found at the scene.
The key point to keep in mind is that the scene will dictate what you need from the suspect. For example, if you find a pair of latex gloves at the scene, process the inside of the gloves for prints, then you will need to swab the hands of the suspect for traces of the powder from those gloves. If the victim was shot, test the suspect for gunshot residue. Keep in mind that this evidence is very fragile, so you can only test for residue if you apprehend the suspect within four hours of the crime. If you find blood at the scene, collect all of it, since some may belong to the suspect. The suspect may have cut himself going in or out of a window. When that happens, be sure to collect samples of the blood and samples of the glass found at the scene. Later, you can match the suspect’s blood to what you found at the scene. You may also find glass from the broken window embedded in the suspect’s shoe or boot. If you have the glass sample from the scene, you can make a match.
Often you’ll find other types of trace evidence at the scene which you can tie to the suspect. Examples include hairs, various kinds of fibers, plant matter, soils, etc. Collect this evidence from clothing, bedding, carpets, upholstered items such as chairs and sofas, and the interiors of cars, etc. Use a vacuum to collect the evidence from carpets, upholstery, and cars. Look for the same evidence on the suspect. If you apprehend a suspect relatively quickly after the crime occurred, you may find trace evidence from the victim on the suspect’s clothing. Alternatively, you may be able to match fibers from his clothing or his hair to trace evidence found at the scene. This kind of evidence may prove crucial to your case.
For some crime scenes, you’ll also need to gather additional evidence. If the victim was sexually assaulted, you’ll need to collect as much evidence as possible from the victim, the scene, and the suspect. The victim’s rape kit should be collected at the hospital or medical center as soon after the assault as possible. At the scene, check all surfaces for evidence of bodily fluids. Once a suspect is apprehended, collect DNA with a buccal swab. Also collect bodily fluids and head and pubic hair samples. For scenes involving fires or bombs, you also need to look for specific types of evidence. At a bomb scene, look for fragments and residue. These may tell you how the bomb was detonated. You may also be able to trace the residue to the suspect, since residue can be found on clothing, shoes, and skin. Suspects will often try to remove residue from their skin, clothing, and shoes. In many cases we can still recover residue from the cracks and crevices of their shoes—places where a suspect can’t see it, but we can still find it. At a fire scene, make sure you test any evidence you find for prints. You’d be surprised at how often a suspect will start a fire with gasoline or kerosene and then leave the container—and his prints—behind.
No matter the crime scene, approach it with professionalism and care. Things like small drops of blood might not seem like much, but they allow you to tie the suspect to the scene. Even if you have what seems like an iron-clad confession from a suspect, you can’t afford to become lackadaisical with evidence. What if the confession gets thrown out on a technicality? If you didn’t bother to collect evidence, your lack of effort will come back to haunt you. Don’t let yourself fall into that trap. Make sure you collect all the evidence you can from every crime scene and suspect. In the end, your efforts will result in solid cases that will hold up in court.
Dick Warrington is in research and development and a crime scene consultant and training instructor for the Lynn Peavey Company.