Fingerprints in Forensics - Searching For Invisible Fingerprints

Just because a fingerprint is not visible to the naked eye, that does not mean that it does not exist. Fingerprints are continuously covered with sweat and naturally occurring body oils that are left behind on everything you come in contact with.

The inside surfaces of your palms, fingers, and even the plantar surfaces of your feet contain friction gyri, or ridges, covered with pores that serve as exit doors for your sweat glands. Even though these particular glands emit sweat that has fewer oils, your fingers no doubt pick up grime, salts, and oils when you touch your hair, face, or any part of your body, like the armpits, that contain more oil-rich sweat glands. Whenever you touch another surface, you always deposit these residues.

The best places where you can find invisible, or latent, fingerprints are hard surfaces. An example of this is a murder weapon, tools or objects left behind or potentially touched by the perpetrator of a crime, opened doors and windows, out-of-place furniture, and drawers. In short, any place that the offender may have touched is a potential source for a latent fingerprint.

The easy approach is the best approach when trying to uncover an invisible fingerprint because of the fact that this approach is the most economical. An angled light source from a penlight, with or without the use of a magnifying glass, may bring it into view. Because the gyrus pattern of an invisible fingerprint actually glows when exposed to ultraviolet light or laser, these light sources may reveal the fingerprints all of a sudden. This same effect is like looking into black-light posters. A print exposed in this way can be documented and then compared with a known fingerprint on a database.

When you watch your favorite CSI program, you will be familiar with this method of using ultraviolet or laser light to discover invisible fingerprints.

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