Prints in crime scene investigations

DEFINITION: Impressions left on surfaces by hands (palm prints and fingerprints) and bare feet (sole prints and toe prints).

SIGNIFICANCE: Fingerprints are routinely collected at crime scenes as means of identifying persons who were present during the crimes, but prints from the soles of feet and the palms of the hands are equally unique and revealing. Any prints that are recoverable at a crime scene may provide information important to the investigation.

Prints from bare feet found at crime scenes can be as telling as fingerprints, but in the United States such prints are less often employed than fingerprints because most people involved in crimes commonly wear some sort of covering—shoes or at least socks—on their feet. Where bare footprints or toe prints are available, they can be as valuable forensically as fingerprints because such prints contain the same ridges and valleys that characterize fingerprints and are as unique to each individual as fingerprints are.

Although bare footprints, toe prints, and palm prints are available less frequently at crime scenes than fingerprints, they can be invaluable to investigators of crimes. Even footprints left by people wearing shoes or socks can be telling in several ways. By measuring the length of a footprint, for example, a forensic anthropologist can arrive at an approximation of the height of the person who left it, because the length of a person’s footprint represents roughly 15 percent of that person’s height.

Palm prints are more frequently available than sole prints and, like fingerprints, the palm prints of each individual are unique. When palm prints are found at crime scenes, the corresponding fingerprints are often present as well.

Fingerprints

Fingerprint analysis is by far the most common way in which law-enforcement investigators connect particular persons with crime scenes. The technology used to accomplish such analysis has advanced considerably through the years. According to a 2024 article in Chemistry World, florescent dyes can reveal fingerprints at a crime scene. Called LFP-Yellow and LFP-Red, the dyes were first isolated in jellyfish. Experts believed they are less expensive and easier to use than other techniques, such as florescent carbon dots and nanoparticles.

When analyzing fingerprints, experts compare certain characteristics visible in the prints collected from crime scenes with the characteristics in prints from known sources to identify the persons who left the crime scene prints.

The basic patterns seen in all fingerprints on record fall into one of three major categories: loop, whorl, or arch. The most common pattern is the loop, which is found in between 60 and 65 percent of all humans. The second most common is the whorl, found in 30 to 35 percent of all people. Approximately 5 percent of people have fingerprints with arches, and a very small percentage have a combination of the three patterns. Primates other than humans also have fingerprints and toe prints that are unique to each individual. Even identical twins have fingerprints different from those of their counterparts, although twins’ prints are often quite similar.

The statistical probability that any two persons’ fingerprints will be exactly alike is virtually zero. No two sets of fingerprints have ever been found to be identical, and fingerprint identification is considered valid in courts of law almost universally.

Even when a person’s fingerprints are damaged by acid, fire, or surgery designed to eliminate them, prints identical to the original prints grow back on the affected fingers in a short time. Some criminals have attempted to destroy their fingerprints, but none has been known to succeed in doing so.

Classes of Prints

The fingerprints, palm prints, and bare footprints collected by forensic scientists fall into three classes: latent, visible, and plastic. Latent prints are those that are made when a hand or bare foot touches any surface, leaving behind a small amount of oily residue. Such prints are not necessarily immediately visible to the human eye, but forensic scientists can enhance their visibility by using a small brush to dust the surface with a powder specifically designed to highlight the ridges and valleys of these prints. After the prints are clearly visible, they are physically lifted from the surface with sterile transparent tape and transferred to special cards for transport to the laboratory for analysis. It is essential that crime scene investigators lift latent prints as quickly as they can, because the residue left behind on surfaces by hands and feet is mostly water and can evaporate very rapidly.

The visible prints found at crime scenes are usually made in some liquid or greasy medium, such as blood or oil. These prints can be seen without magnification. Plastic prints are those that are recovered from malleable materials, such as unfired clay or pastry dough. Both of these types of prints are photographed, and the photographs are transferred to print cards.

Forensic Uses of Footprints

In addition to suggesting the height of the person who made them, bare footprints or shoe prints made in sand or other soft surfaces can reveal the person’s weight, through the depth of the impressions. Forensic scientists preserve such impressions by making plaster casts of them, and analysis of such casts often provides convincing linking particular individuals to the scenes of crimes.

The foot impressions found at crime scenes are more often shoe prints than bare footprints, but shoe prints can also provide valuable information. Both footprints and shoe prints, for example, can reveal the direction in which the people who made them were traveling and approximately how fast they were moving (the prints left by the two feet of a person who is walking are closer together than the prints of a person who is running). The depth of foot impressions can suggest the weight of the person who left them and may also reveal whether the person was carrying something heavy.

Both shoe prints and bare footprints can reveal information about gait—that is, the way a person walks—that may help investigators to identify an individual. The angles of such prints, for example, can suggest the age and physical condition of the person who made them, such as whether the person is elderly or suffering from a condition such as arthritis.

Palm Prints and Sole Prints

When bare footprints are found at crime scenes, they are generally found in sand or in soft earth. Crime scene investigators must preserve and collect such prints immediately, as they can quickly be degraded and washed away by rain, wind, or tides.

Footprints are generally much less commonly found at crime scenes than are fingerprints. Sometimes bare footprints are retrieved as visible prints from crime scenes where considerable blood has been shed, and in such cases they can provide strong evidence of the presence of particular persons at the scene. In similar situations where only shoe prints are found, the shoe prints can provide suggestive evidence that generally falls short of being incontrovertible.

Latent fingerprints are more likely to be recovered from crime scenes than are latent palm prints, although, in some instances, investigators are able to collect both fingerprints and palm prints. In cases in which a person committing a crime has grabbed a cylindrical piece of wood, such as a bedpost, both latent palm prints and fingerprints can often be retrieved.

Bibliography

Bell, Suzanne. Encyclopedia of Forensic Science. Facts On File, 2004.

Bodziak, William J. Footwear Impression Evidence: Detection, Recovery, and Examination. 3rd ed., CRC Press, 2013.

Conklin, Barbara Gardner, et al. Encyclopedia of Forensic Science: A Compendium of Detective Fact and Fiction. Oryx Press, 2002.

Corless, Victoria. "New Spray-On Dyes Can Instantly Reveal Fingerprints at Crime Scenes." Chemistry World, 2 Feb. 2024, www.chemistryworld.com/news/new-spray-on-dyes-can-instantly-reveal-fingerprints-at-crime-scenes/4018872.article. Accessed 19 Aug. 2024.

Hilderbrand, Dwane S. Footwear, the Missed Evidence: A Field Guide to the Collection and Preservation of Forensic Footwear Impression Evidence. 2nd ed., Staggs, 2005.

Panchal, Vijay and Rakesh Mia. "Detection of Footprint Impressions at the Scene of a Crime--A Review." Journal of Forensic Sciences and Criminal Investigation, vol. 15, no. 4, 21 Mar. 2022, DOI: 10.19080/JFSCI.2022.15.555919. Accessed 19 Aug. 2024.

Pentland, Peter, and Pennie Stoyles. Forensic Science. Chelsea House, 2003.