Summary
Highlights
Latent print analysis is a fundamental and long-standing forensic science discipline used for individual identification, dating back to the late 1800s. The latent print unit assists law enforcement by using the unique characteristics of fingerprints, handprints, and footprints to identify individuals connected to criminal activities or to identify unknown deceased persons.
Finger and palm prints are unique to every individual, even identical twins. Perspiration from glands on the ridges transfers print impressions to surfaces. Latent print evidence is categorized as porous (e.g., paper, cardboard) or non-porous (e.g., glass, metal). Prints can be visible (blood, grease, dirt), semi-visible (glass), or invisible to the naked eye.
Visible and semi-visible prints can be viewed by light modification or powder treatment. Invisible prints pose a greater challenge, requiring techniques such as exposing non-porous objects to cyanoacrylate esters (superglue fumes) in a chamber, or a vacuum-sealed chamber for larger objects. For porous materials like paper, a chemical dye and warm moist air are used. Another method involves dusting with a chemical and exposing it to ultraviolet light. All revealed prints are photographed for examination.
Latent print examiners analyze details like loops, whorls, and arches. If enough information is present, the unknown print is compared to known samples. Continuous agreement without unexplained differences leads to a positive identification. If no known sample is available, the print is compared with the AFIS (Automated Fingerprint Identification System) database, which holds millions of records. If state searches are inconclusive, a national FBI system can be used. Unsolved prints can also be entered into an unsolved latent database, which is continuously searched.
The latent print unit also identifies unknown human remains, obtaining prints from decomposed or mummified fingers and palms. These are compared with the AFIS database or prints from personal belongings of missing persons. Latent print identification provides law enforcement with undisputed evidence, remaining the most widely used technique due to the vast resource of known fingerprints.