Many do not understand what goes into either the search for latent fingerprints, or the methods of identifications. Perhaps this will help better understand.
First, what are fingerprints? Look at your hands. Notice how the skin on the palms and fingers (and also the bottom of the feet and the toes) is different from the rest of the body. Our bodies have adapted to the needs of our abilities by forming ridges along these surfaces. These ridges are designed to create friction, to aid in walking and in handling items with our hands. If you continue to look, you will see that these ridges are not symmetrical; they flow into formations, all the while individual ridges abruptly stop, merge into other ridges, or may even be represented as just a dot. These formations and individual details provide the basis for the uniqueness of the prints, permitting their use as an individual form of identification. Along the summits of these ridges are located pores, through which the body exudes waste chemicals both to rid the body of them and to provide for bodily temperature stabilization, the waste commonly referred to as perspiration or sweat. This sweat is made of a number of chemicals, including water, fats, and amino acids. As with all skin, unless severely damaged, it will repair itself, resulting in the permanence of the ridges as an identification tool. From gestation until post mortem decomposition, the ridges will remain intact, unless the dermis is so badly damaged that it results in scarification.
Fingerprints are deposited in one of three manners. First, one may touch a plastic material, for example putty, and impress the fingerprint onto this material. Second, one may touch a material like paint or blood, and transfer the image of one’s fingerprint to another surface. Finally, the sweat mentioned above spreads along the top of the fingerprint ridges; when we touch another surface, we transfer the image on the fingerprint to that surface as a usually invisible transfer.
Fingerprints vary among individuals. We each have different skin; various factors result in their being ethno-anthropological differences in skin, so that some groups produce deeper furrows than others. We all have slightly different chemical make-up, and our bodies exude sweat differently, and with different chemical make-up that affects is composition and quantity. For many of us employment has effects on our skin; various trades work with chemicals which have destructive effects on the body and its ability to produce the sweat. Each of these factors will effect the potential for any one of us leaving “latent” fingerprint, composed of sweat, or “patent” (transfer) or “plastic” (impressed) prints.
Other factors affect the potential of locating prints. An easy one is cleaning. When an area is wiped down, prints are destroyed. Another is environmental conditions. High temperatures and low humidity each work to hurry the evaporation of fingerprint material. Similarly winds will aid in evaporation of the materials. In hot summer sun, especially with a breeze, latents deposited on a surface such as a metal auto body, will very quickly be aged, and their detection hampered if not stymied. Yet in protected areas, a latent may remain for almost indeterminate periods of time, full of life as its oils and other constituent components are not harmed.
Different surfaces also affect the location of fingerprints. Slick, non-porous surfaces tend to permit easy development of latents, using traditional powder techniques, assuming environmental factors do not harm them. Thin plastic material such as plastic bags requires other techniques to visualize the prints. Porous materials generally require chemical processing – paper products are often processed with ninhydrin, an amino reactive chemical, iodine fumes which react with the fatty components of the sweat, or silver nitrate which reacts with the salts in the sweat. While blood is often thought of as a red liquid, much of it is a clear liquid, and a variety of chemicals are used to visualize fingerprints transferred in it.
Thus it is far from just dusting a surface to locate a print. Even a beautiful, slick, non-porous surface may host latents that will not adhere to dust. This is where an experienced fingerprint specialist is of value, knowing the variety of techniques and how to use them, to permit searching surfaces that may hide damaged or dried out latents.
Identification of fingerprints is another misunderstood aspect. Since about 1980, automated fingerprint identification systems have been established that permit “cold” searches of latents. However, currently these systems are only available to the agencies that comprise the criminal justice system; they are generally not available to civil case practitioners due to various privacy laws. Thus in civil work one is limited to comparing against known standards. These may be available from police or regulatory agency files, depending on privacy laws. For clients and cooperating persons inked standards may be obtained. A common misconception is that one may surreptitiously obtain prints from a suspect by having them handle an item and then process it for latent prints. However, this is an especially inefficient method. First, will the suspect deposit all ten fingers on the item? Second, how well with the suspect handle it, how complete will be the latents left behind. What is being done is comparing latent prints to latent prints – and if either is incomplete, or if the “standards” do not include all ten fingers, it is very possible that the finger or area of finger involved will not be obtained to compare against the unknown print.
Records searches should be conducted against suspects; if either regulatory licensure is found, or a criminal arrest history, attempts should be made to obtain certified copies of the record fingerprints from the record keeper. Perhaps non-public agency fingerprints exist; some employers maintain fingerprints in their records for any of several reasons. Perhaps these may be obtained for comparison. Much like computer work, fingerprint comparison is a garbage in, garbage out proposition – if the “standard” is of low quality, the potential of identifying a latent decreases significantly.
Associate with a fingerprint specialist; their counsel will help you make the early decisions on how to proceed with an evidence examination much easier in the log run.
