What do fingerprints identify

Analysts classify fingerprints into three categories according to the type of surface on which they are found and whether they are visible or not: Fingerprints on soft surfaces such as soap, wax, wet paint, fresh caulk, etc. Visible prints are formed when blood, dirt, ink, paint, etc. Patent prints can be found on a wide variety of surfaces: smooth or rough, porous such as paper, cloth or wood or nonporous such as metal, glass or plastic.

Latent prints can be found on a variety of surfaces; however, they are not readily visible and detection often requires the use of fingerprint powders, chemical reagents or alternate light sources. Generally speaking, the smoother and less porous a surface is, the greater the potential that any latent prints present can be found and developed.

Patent prints are collected using a fairly straightforward method: photography. These prints are photographed in high resolution with a forensic measurement scale in the image for reference. One of the most common methods for discovering and collecting latent fingerprints is by dusting a smooth or nonporous surface with fingerprint powder black granular, aluminum flake, black magnetic, etc.

If any prints appear, they are photographed as mentioned above and then lifted from the surface with clear adhesive tape. The lifting tape is then placed on a latent lift card to preserve the print. However, fingerprint powders can contaminate the evidence and ruin the opportunity to perform other techniques that could turn up a hidden print or additional information. Therefore, investigators may examine the area with an alternate light source or apply cyanoacrylate super glue before using powders.

Alternate Light Source ALS : It is becoming more commonplace for investigators to examine any likely surfaces doors, doorknobs, windows, railings, etc. These are laser or LED devices that emit a particular wavelength, or spectrum, of light. Some devices have different filters to provide a variety of spectra that can be photographed or further processed with powders or dye stains.

For example, investigators may use a blue light with an orange filter to find latent prints on desks, chairs, computer equipment or other objects at the scene of a break-in. Using a fluorescent dye stain and an orange alternate light source helps this latent print appear clearly so that it can be documented.

Use of various alternate light sources may help enhance the appearance of a fingerprint. Cyanoacrylate: Investigators often perform cyanoacrylate superglue processing, or fuming, of a surface before applying powders or dye stains. This process, typically performed on non-porous surfaces, involves exposing the object to cyanoacrylate vapors.

Reacts with amino acids in the fingerprint to stain the fingerprint pattern deep blue or purple on paper and other porous surfaces. Developed as a safer, cheaper alternative to 1,8-diazafluorenone, which was popularly used to develop fingerprints on porous surfaces. Both reagents make fingerprints glow when hit by certain wavelengths of light. Forensic technicians typically visualize the prints by dusting them with powder and lifting them with adhesive tape, using a dye stain, or fuming the area with cyanoacrylate vaporized superglue.

The prints are then photographed or scanned. At that point, an examiner must decide whether a collected print is good enough to attempt an individualization. This means comparing the latent fingerprint with a fingerprint from a known subject and determining if there is enough information in the ridges and whorls to suggest both samples were left by the same person.

Forensic scientists use the term individualization instead of the word match because the analysis is about probability, not necessarily certainty. Some of the remaining prints are compared manually by a human fingerprint analyst, and the rest—smudged or otherwise corrupted—are simply stored as evidence, often pressed between the adhesive tape used to lift them and a paper backing card.

For decades, fingerprint individualization was the only reason for lifting latent prints from a crime scene. She brought the project to Dawson Cruz with the hope that she would be able to find a way to extract usable DNA from the archived samples—samples that had been sealed away simply to preserve their ridge patterns, with no consideration given to conserving genetic information.

Dawson Cruz found that the type of black powder used to dust for prints in did not significantly interfere with her ability to extract DNA from them; neither did cyanoacrylate fuming. In fact, the DNA, housed in skin cells, was protected and preserved in its tape-and-card sandwich. The challenge was to remove the DNA from the substrate while minimizing damage and loss of genetic material and while isolating and concentrating as much of the sample as possible.

Dawson Cruz and colleagues examined every part of the DNA-extraction process with an eye toward optimizing protocols and getting as much usable genetic information from archived fingerprints as possible J. Forensic Sci. Working with fingerprint samples ranging in age from 0 to 28 years old, the VCU team found they could extract the most skin cells, and thus DNA, by pulling apart the fingerprint sandwich of tape and paper, cutting each layer into strips, and then immersing the strips in a solution designed to break open cell membranes and release the DNA.

These discoveries, as well as other recommendations, could have broader implications for improving the analysis of DNA from fingerprints in present-day investigations, Dawson Cruz says. That area of research is young—beginning in the late s—and forensic scientists are still working out the kinks. As Dawson Cruz is looking to extract genetic information from aged prints, other researchers are looking to make better use of those smudges by examining other chemicals contained within.

The group first used these analyses to distinguish between samples from female and male sources; amino acid levels are known to be roughly twice as high in the sweat of females as in males. More recently, the researchers published work showing they could use the levels of metabolites in sweat to distinguish between samples from two different people, regardless of sex Anal. The advantage of the assays, he says, is that they can analyze samples at the crime scene more rapidly and cheaply than DNA testing.

So they could be used to determine quickly whether a particular print is from a man or woman or identify whether multiple people were present at a crime scene. The shortcoming, though, is that, unlike DNA, metabolite levels fluctuate according to age, activity level, and other factors, so the assays would be unable to pinpoint the identity of a suspect.

The assays can be run with less than a droplet of sweat, leaving the rest of the sample for later lab tests. The chemicals in fingerprints left on the outside of the package can offer clues. But the portable ion mobility spectrometry instruments that agents typically use to screen for explosives employ high temperatures to vaporize the chemicals in question and would destroy traditional fingerprint-lifting materials, like adhesive tape.

So if the package did turn out to be a bomb and agents had already screened the print for explosives via standard methods, its pattern would be too damaged to help track down who left it there. Staymates and colleagues wanted to develop a method that would analyze a fingerprint for chemical residues while preserving its pattern.

After testing several combinations, they settled on a white Teflon strip paired with a high-temperature adhesive originally created for aerospace use. They proved that it worked by creating prints with artificial fingers molded from ballistic gelatin that had been pressed into simulated plastic explosives Int. Ion Mobility Spectrom.

Importantly, the print pattern stayed intact and could still be used for identification. And no other scientists had replicated their findings. Research takes time, and Marcus Ray Johnson was running out of time. Miller testified that the team had been able to extract usable DNA from archived fingerprints as much as 20 years old. Johnson was executed on Nov. There has long been a need in the forensic science community to research new ways to analyze crime-scene evidence, especially since , when the National Academy of Sciences published a report asserting that many forensic disciplines—fingerprint analysis included—have little or no scientific underpinning.

The report drew a skeptical eye to a field in which validity had long been assumed rather than proved. Read the original article. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Lecturer in Chemistry, University of Surrey.

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