Are all fingerprints truly unique?
Yes. It has to do with how the fingerprints form in the womb. During the first trimester, the fingerprints have already established their permanence and uniqueness.
Aside from forensics and travel, what else are fingerprint scans being used for these days?
More and more, fingerprints are being used in biometric devices to permit secure log-on, to open locks, and for access control in general. The biggest users of biometrics are corporate and private users, but fingerprints also have a long history in the forensics world for criminal identification dating back over a century.
Are current scanners pretty reliable?
The exact rate of print rejection [those that can't be read] depends on the scanner. Ultrasound devices go beyond just the outer layer and capture part of the root system. On average, the rejection rate for [scanned] fingerprints is about 1 to 2 percent.
The patient who was detained for lacking prints had hand–foot syndrome that was caused by his chemotherapy drug. What are some other ways that fingerprints can disappear?
The most prominent of those problems involve bricklayers—who wear down ridges on their prints handling heavy, rough materials frequently—or people who work with lime [calcium oxide], because it's really basic and dissolves the top layers of the skin. The fingerprints tend to grow back over time. And, surprisingly, secretaries, because they deal with paper all day. The constant handling of paper tends to wear down the ridge detail.
Also, the elasticity of skin decreases with age, so a lot of senior citizens have prints that are difficult to capture. The ridges get thicker; the height between the top of the ridge and the bottom of the furrow gets narrow, so there's less prominence. So if there's any pressure at all [on the scanner], the print just tends to smear.
How have people intentionally changed or "disappeared" their fingerprints?
There are many documented cases of intentional fingerprint mutilation, but generally those involve pretty severe damage to the skin—more specifically between the generating layer, where the template of the fingerprint survives, and the upper layer, the epidermis.
Pretty much any cut or burn that goes deeper than the outer layer of the skin can affect the fingerprint pattern in a permanent way. But even with permanent scarring, the new scar becomes a unique aspect of that person's fingerprint.
The first case of documented fingerprint mutilation was in 1934, by Theodore "Handsome Jack" Klutis, who led a gang called the College Kidnappers. When the police finally caught up with him, Klutis went for his gun and the police returned fire, killing him. When they compared his postmortem fingerprints, police found that each of his prints had been cut by a knife, resulting in semicircular scars around each fingerprint. Although it was glorified in the media, it was an amateur job; the procedure left more than enough ridge detail to identify him.