Crime Scene Fingerprints

Just because a person touches something doesn't necessarily mean he or she has left behind a latent print. Not all surfaces are receptive to finger marks. For example, it is particularly difficult to retrieve a latent print from rough-surface wood, cloth, skin, cardboard, and Styrofoam. Finger marks can also be incomplete (called partials), smudged, smeared, or on top of each other. Smooth, shiny surfaces are the best sources for clear, complete latents suitable for comparison and identification. At the crime scene, these latents can be brushed with a fine powder and lifted from the surface with strips of transparent tape. It is not a perfect process and can be a hit-and-miss proposition. Ideally, removable objects that may contain the perpetrator's latents--drinking glasses, bottles, cans, guns, cigarette butts, knives, shell casings and the like--are best sent to the crime lab where special equipment and techniques can make the marks visible for expert analysis. The same goes for grocery bags, sheets of paper, envelopes, notebooks, and magazines that might carry latent prints. Finger marks on countertops, furniture, doorknobs, cellphones, automobiles and window glass are usually lifted at the scene. Latents that can be seen by the naked eye--for example, prints in safe insulation dust, blood, wet paint or soot--should be photographed where they are found.