Southern California Association

General Information About Fingerprints
(Friction Ridges)

Q. What is friction skin?
A. Present on the inner (palmar) surface of the hands and fingers and the bottom (plantar) area of the feet is skin that is different from the skin on other areas of our bodies. This skin is rough or corrugated, consisting of raised portions that we call ridges. These ridges do not run continuously from one side to the other, rather, they may curve, end, and split or divide in two or more ridges. These ridges aid the finger's ability to grasp by increasing friction, thus the term friction skin.

Q. What is a latent print?
A. Present on the tops of the friction skin ridges are very minute sweat pores that are constantly exuding perspiration. This perspiration adheres to the outline of these ridges. Other substances, like oil from touching your face or hair, can also adhere to these ridges. When an object is touched, a recording of these characteristics may be left upon the surface. At times, these impressions will be visible, and at other times they will be invisible; thus the term "latent". Although visible prints are truly patent prints, they are frequently referred to as latent prints. The invisible latents must be developed or made visible either by the application of powders, chemicals, or electronic means.

Q. What is an inked fingerprint?
A. An inked fingerprint is a reproduction of the ridges of the finger with black fingerprint ink on an exemplar form.

Q. What is the scientific basis for fingerprint identification?
A. Fingerprints are permanent and unique. Fingerprints are formed before birth and last throughout one's life until decomposition after death. Barring accidental or intentional mutilation, the ridge arrangement is permanent.

Q. What is a latent print examiner?
A. A Latent Print Examiner must be knowledgeable in all areas of the science of fingerprint identification including history; methods of classifying; and procedures for locating, processing and preserving latent prints at the crime scene or in the laboratory. Latent print examiners present expert witness testimony in all phases of the science of fingerprint identification.

Q. Can a latent print examination be conducted in the courtroom?
A. No, latent print comparisons involve a concentrated study of minute ridge detail and should be conducted in an environment free from undue pressure or distractions. Also, scientific protocol requires that all latent print identifications be verified.

Q. What is an identification?
A. An identification is made when, in the judgment of the examiner, the degree of similarity between the two prints is sufficient to warrant that conclusion. The result of any comparison is the opinion of the examiner based on training, experience, and understanding of the science.

Q. Is an identification determined by matching a specific number of points (ridge characteristics)?
A. There is no valid scientific or any legal basis for requiring a minimum number of matching points (ridge characteristics) needed to effect an identification. Conclusions are not based solely on the number of matching points of similarity, but on a series of observations involving a thorough examination of minute ridge detail.

Q. Does the lack of latent prints on evidence mean that the object was not touched or that the prints were wiped off?
A. Failure to recover latent prints does not mean that the prints were wiped off or that the object was not touched. The absence of latent prints can be caused by various factors, each depending on conditions existing before, during, and after the finger touched the object.

Q. Can the age of a latent print be determined?
A. There is no known scientific test available today to determine the age of a latent print.

Q. What is "CAL-ID"?
A. "CAL-ID" is an automated fingerprint processing system used to store, search, and retrieve fingerprint records. CAL-ID has two systems in operation: Automated Fingerprint Identification System (AFIS) and Automated Latent Print System (ALPS). AFIS automates fingerprint data from inked fingerprint cards while ALPS searches latent prints for possible matches.

Q. Do computers like the CAL-ID System make latent fingerprint identifications?
A. No. Identifications are determined by qualified fingerprint examiners. A computer simply provides or generates a candidate list of possible matches.

Q. What is "Forensic Digital Imaging"?
A. Digital imaging refers to the placing of photographic or visual information into digital form using sophisticated digital cameras or flatbed scanners. For the latent print examiner, this means entering digital images of inked, powdered, and chemically developed latent prints into a computer. The result of digital enhancement (adjusting the brightness, contrast, density) of the various images allows the examiner, using imaging software to improve the clarity of the images, to better formulate conclusions.