How to Fingerprint in Forensic Science

Fingerprints are an invaluable tool for law enforcement officers.

Fingerprinting a subject is a basic skill for law enforcement officers and forensic specialists. A person training to work in law enforcement should practice fingerprinting before he attempts it on a real subject. Fingerprinting may be tricky; you need to cover the finger with just the right amount of ink or the impression may be too faint or too smudged. You'll also need to practice evenly rolling the finger on the fingerprint card. Don't feel discouraged if the impressions appear smudged on your first attempt. With practice, you'll get the hang of it.

Difficulty:

Moderately Easy

Instructions

Things You'll Need

• Alcohol swab
• Lotion
• Ink
• Fingerprint card

1. Check the fingers. They need to be dry and clean. If perspiration is a problem, wipe the fingers with an alcohol swab and dry them. If the fingers have rough surfaces (which can occur with manual labor occupations), wipe a lotion on them, then wipe the lotion off. This should soften the rough patches.

2. Place the ink and the fingerprint card on a flat surface. The FBI recommends that the surface be high enough so that the subject's forearm can be straightened toward the surface, while being parallel to the floor. This will prevent any inaccuracies in the printing.

3. Stand behind the subject, as well as a little off to the right. Grasp the subject's right hand. The finger that you are printing first should be extended. Use your hand to tuck under all the other fingers.

4. Roll the subject's finger on the ink pad. Ensure that the entire area is covered with ink. However, do not use too much ink, or the impression will lose detail. You may need to practice this a few times to get the hang of the proper technique.

5. Place the side of the bulb of the inky finger on the fingerprint card. Roll it evenly so that the whole fingerprint is left on the card. Repeat this process with all the fingers. When printing the left hand, stand a little to the left of the subject.

6. Take plain impressions last. A fingerprint card has a section for rolled impressions and one for plain impressions. According to the FBI, plain impressions are pressed, rather than rolled. Simultaneously press four fingers on one hand onto the appropriate area. Repeat this with the other hand. Press both thumbs last.

Tips & Warnings

• If the subject has a bandage on the hand, or similar obstacle to fingerprinting, write "UP" in that finger block. This stands for "unable to print."

References

• FBI: Taking Legible Fingerprints

Resources

• NOLO: Fingerprint Evidence: What You Need to Know