|MadSci Network: Genetics|
Hello Callie, CSI makes forensic science seem magical at times, doesn't it. Unfortunately, in the real world, the magic runs out and we are forced to use real science, good techniques and hard work. Fingerprints, or more properly, latent prints, are not always left behind at a crime scene. The deposition of latent prints depends on conditions such as temperature, humidity, and type of surface touched. The use of gloves will naturally deter the deposition of a latent print. We have found that latent lifts are deposited well on clean, hard, dry, smooth surfaces such as glass, metal, smooth hard plastic, and paper. Latents are not deposited well on textured surfaces such as molded plastic gun grips, molded plastic dashboards and automobile trim, wet surfaces, or fabric clothing. Different processes are used to develop and enhance latent prints. Your mentor will be able to show you super glue fuming, dusting with black/white powders, use of fluorescent dyes and alternate light source enhancement. A nice experiment is to take your finger and rub your forehead, then touch a smooth surface such as a piece of glass or a mirror. You will leave behind a nice, detailed latent print. The latent consists of mostly water and salts plus some oils. Wash your hands well with soap and water, dry them, then repeat the process. The latent, if present, won't be nearly as evident. You've removed the oils from your skin and lessened your chance of leaning behind a latent. Another experiment that you can do will test the affect of age on a latent. An examiner can never determine when a latent was deposited. However, as latents age, they dry up, and become harder to see. To test this, place several latents on a clean plastic or glass surface in a row. Process the first latent (far left) one day, the second one week later, the third one week after that, and so on. Sometimes, we find latents in blood. This is very good evidence because it places that individual at the scene when blood was shed. However, being a liquid, blood sometimes smears. A nice experiment that you can do is to test how long after blood is shed will you leave behind a latent of value (with ridge detail). To do this, you will have to prick your finger with a sterile needle (have your Mom or Dad help you :-). It just needs to be a little stick. Start a second timer and begin to touch a clean piece of glass or plastic trying to leave behind a latent. The first ones will appear "runny" and smeared. But as the blood dries on your finger, it gets sticky, and you will begin to leave behing latents with fantastic detail. Eventually, the blood completely dries up, and you no longer will leave behind a latent at all. So you can show how limited the time period is in which you can leave behind a bloody latent with ridge detail. It's really just a few minutes. Another experiment that you can easily do is to put on a pair of latex surgeon's gloves (the thin ones doctors and nurses use). Criminals sometimes where gloves when they commit a crime. Try and leave behind a latent on a piece of glass. Initially, you won't be able to. But continue to wear the gloves and exercise, run in place, etc. Remember, criminals are sweating and in a hurry. As time goes on, you will notice that you can begin to leave behind latents through the gloves, especially if you press hard. The oils and water seep through pores in the gloves and leave behind trace latents. I hope this helps. Sounds like you will have an interesting and fun project. Good luck. Best regards, Dale L. Laux Forensic Scientist
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