Fingerprinting remains the primary way to identify suspects for law enforcement. Police officers must use proper equipment and techniques to get the best finger print rendering. Here is how to take fingerprints.
“Prepare the Suspect’s Hands”
An officer should carefully inspect the suspect’s hand first. Are there any permanent deformities, such as missing sections, cuts or abrasions? Are there temporary conditions, like blisters, callouses or dryness? The suspect should wash his or her hands, cleaning them dry with an alcohol wipe.
Equipment needed includes heavy black paste ink, smooth glass inking plate, identity card and roller. The officer should apply a few dots on the smooth glass and roll it out evenly until it has a dull finish. The black ink should cover a three-inch-by-three-inch area.
Officers should position themselves to the left of the suspect when inking the right hand. Each finger should be done separately in the proper order. Officers should hold the finger at the tip of the nail and base of the finger. The officer should tell the suspect to “Relax” to get the best rendering. The officer should hold the finger firmly and lightly press down on the pad to make the impression.
“Arch Loop Whorl and Delta”
Roll the finger from the most difficult position to the most easy position. The perfect finger print has clearly identified black ridges and white valleys showing the full finger up to the first joint. The Automated Fingerprint Identification (AFS) system encourages clearly identifiable bifurcations. When printing the thumb, it should be rocked forward.
Avoid smudges by making a clear pass rolling and not dragging or twisting the finger. Law enforcement will look for finger prints that have certain identifiable patterns, such as “Arch has No Delta” and “Whorl has Two Deltas.”
Fingerprinting is both a science and an art. Once a good print is made, computers can quickly compare the image to those stored in its database. This all begins with a good finger print technique. There are also law enforcement agents who will take palm prints: upper, lower and writer’s.
Once completed, the equipment should be stored away from places where dust and lint can collect. Water-based ink may run, so a heavier ink paste consistency is preferable.