Fingerprints form before birth and, except for cuts resulting in permanent scars and diseases such as leprosy, remain unchanged until the body decomposes after death.
Fingerprint evidence is the most positive investigative means of identifying people. Even DNA blood analysis cannot differentiate between identical twins – fingerprints can. Every fingerprint is unique. Fingerprints are records of the raised surface of papillary skin, also called friction skin, appearing on the palmar side of a person's fingers.
Papillary skin is present on the palmar surfaces of the hands and the plantar surfaces of the feet. These are skin surfaces on your fingers and hands which touch a drinking glass with when you pick it up, and the skin surfaces on your toes and bottoms of your feet which touch the ground when you walk barefoot.
Palm, lower finger joint, sole and toe impressions are all unique. Almost any area of friction skin that can be covered with a pencil eraser is large enough to permit positive identification if recorded clearly and completely.
Although many fingerprints have the same pattern type and look very similar, when examined closely the differences can prove that the prints have been made by different fingers. And the opposite may be true. Prints from the same finger may look different because the pressure used to make them differed. Or they may look different because the curve of the surface differed. Yet examination by a qualified examiner can prove the prints to have been made by the same finger.
Positive identification or elimination of fingerprints can only be made by trained and qualified fingerprint examiners. Examiners identify prints by making the qualitative and quantitative comparisons of one friction ridge print with another. They compare the separate ridge characteristics and their relationship one to another. They can do this from impressions of any area of friction skin.
Fingerprint records are maintained in civil and criminal repositories in America. Civil fingerprint identification, such as occurs with police or soldiers entering into public service, is the recording of a person's fingerprints primarily for the purposes of:
- Determining the person has no prior criminal arrest record
- Verifying the person's identity at a later date
Criminal fingerprint identification is the recording of an arrested person's fingerprints primarily for the purposes of:
- Recording the arrest and/or conviction information in a permanent file associated with that person
- Determining the person's true identity if they have used other names for previous arrests
- Determining the person's prior arrest/conviction record
Recording Inked Prints
Fingerprints impressions taken directly from a person's fingers for the purpose of identification must be uniformly clear and visible. It is not hard to take good, clear fingerprints. A good fingerprint impression is dark gray in color and free of smudges. All that is needed to obtain good prints is practice.
The steps for inking fingers and the steps for making impressions on the card are the same. Each finger is rolled through the ink on the glass and then that finger impression is rolled on the fingerprint card. All rolling should be made in single movements. The pressure should be just enough to apply an even coat of ink on the finger and a clear image on the card.
Note that children below the age of 8 years may not have fully developed friction ridges. It is advisable on young children to record palm prints instead of fingerprints.
Rolled Impressions are made by rolling the finger or thumb from nail edge to nail edge. This surface gives all the needed ridge characteristics for correct classification. (Classification is the means by which a set of fingerprints may be filed and then retrieved in the future.)
There is a specific means of rolling the subject's fingers or thumbs in the ink and on the fingerprint card to give a good impression. You roll the fingers or thumbs from “awkward to comfortable.” To see what is meant, hold your hands in front of you with the backs of your hands together. Now roll them around so that the palms are together and thumbs are up. You will see that the right hand moved clockwise and the left hand counterclockwise. This is the direction the fingers on each hand should be moved. Thumbs are moved in the opposite direction of the fingers.
Plain impressions verify the order of the rolled impressions and show characteristics that are sometimes distorted in rolled prints. Plain impressions are made on the card by just pressing the four inked fingers on the card at a slight angle. They should show from the tips to one-fourth inch below the first joint. Thumbs are then printed by inking and pressing them on the block next to the plain finger impressions.
Have the subject hold his fingers straight and stiff. The hand should be level with the wrist. Grasp the wrist with one hand and press the fingers onto the cards with the other hand. Then allow the subject to clean the ink from his fingers.
Excessive perspiration may cause inked impressions of many persons to blur. Wipe each finger with a cloth and then quickly ink and roll it on the fingerprint card. Follow this process with each finger. You may also wipe the fingers with alcohol or other drying agent. Some people have dry, rough hands from their work. Rubbing the tips of the fingers with oil or creams can often make them soft enough for clear, unsmudged prints. If the ridges are fine and small and the skin is soft, holding ice against the fingers sometimes helps.