A study on the effects of time and temperature on the recovery of latent prints from computer paper and plastic bottles.

Fingerprints are considered one of the most reliable ways to identify individuals associated with criminal cases. However, sometimes they cannot be recovered due to various environmental factors. One of these factors is temperature, specifically high temperatures. At high temperatures the water left by fingerprints evaporates and the amino acids denature. In this experiment, the optimal temperature ranges for a sheet of computer paper and plastic bottle was found to be from -20°C to 185°C for a 15 minute exposure to heat and from -20°C to 150°C for an hour exposure to heat.

Background
Fingerprints are widely accepted as being a unique characteristic of a person. Kaushal states, “No two people, not even identical twins, have ever been shown to have exactly the same pattern of raised, curved lines on their fingertips.” ¹ These patterns on the fingertips, called minutiae, are special to each individual person. When a person touches a surface, a chemical mixture of their fingerprint is left behind called an impression, which refers to the friction ridge detail deposited on the surface. If this action is unintentional, it is called a latent print. In most cases, fingerprint examiners deal with latent prints. The mixture that makes up these impressions include water, amino acids, cholesterols, fatty acids, small-molecule oils, DNA, and ionic salts.² Forensic scientists use numerous techniques to react with these chemicals and make the latent print visible to the naked eye.

Several factors can alter or disrupt these chemicals and therefore make the latent print unidentifiable to an examiner. The temperature of the surface on which a latent print is left is one such factor.³A higher temperature would cause the water to evaporate and cause the amino acids to denature. This can make the latent print hard to visualize and extremely difficult to identify. A study done by William and Karen Sampson⁴ suggests that the optimal temperature ranges for identifications are from 68°F to 95°F (20°C to 35°C). The study suggested that if a latent print was exposed to heat or dryness for hours to days, it would be hard to retrieve the print.

The purpose of the present study is to determine the optimal temperatures in which a latent print can be recovered from a piece of computer paper and a plastic bottle. Paper and plastic were chosen because they are commonly handled by individuals on a daily basis. Also paper and plastic are commonly found at crime scenes. Once the range is determined, the time period in which the latent print endures those temperatures will be extended to see if the range shortens.