For well over a century, fingerprints have been at the cornerstone of forensic investigations in America. Globally, the concept of fingerprint identification dates back even further, with thumbprints used to sign contracts in Babylonian times. The resilience of this method of identification comes down to a powerful tenet that’s yet to be disproven: no two sets of fingerprints are the same.
While the underlying logic is the same as it’s always been, the technology around fingerprinting has changed drastically in the last hundred years. Up until the late 1960s, fingerprints were compared optically: investigators would compare one set of prints against dozens or even thousands of others and try to find a match, using nothing but their eyes. While laborious, it was effective. Today, the FBI can match a single fingerprint against millions of others in under ten minutes.
Fingerprinting has come a long way since it was first used to sign contracts thousands of years ago, but some of its most fundamental principles haven’t changed at all. To get a detailed look at what fingerprints can and can’t tell us, read on.
Identical twins are coded to be practically indistinguishable. Split from the same fertilized egg, they share the same genetic makeup, which gives them the same sex, and in most cases the same hair color and same eye color, too. But identical twins will never have the same fingerprints.
Fingerprints, like the patterns in one’s palm, are initially formed in the womb. Slight differences in the placement, pressure, and position of a fetus’s hands all affect the development of their fingerprints. As each identical twin’s body continues to grow and experience slightly different environmental factors, their fingerprints will diverge further and further, forming their own unique characteristics.
Thanks to their genetic coding, identical twins will usually share certain characteristics in their fingerprints—a similar combination or arrangement of arches, loops, and whorls, for example—but they will always be identifiably different.
DNA fingerprinting, also known as DNA profiling, isn’t really fingerprinting at all. Instead, it refers to the identification of an individual by matching them to a DNA sample. While everyone shares over 99 percent of the same DNA traits, what remains is highly individualized. By taking a sample of found DNA, and comparing it with DNA taken from an individual, one is able to determine whether there is a match between the two with a high level of confidence.
DNA fingerprinting is a sophisticated technological process, but sometimes it’s not as robust as more analog methods of identification. In 2004, a DNA sample taken from a potential parolee was matched to a serious crime committed five years earlier. It should’ve been an open and shut case, but the suspect whose DNA matched the crime scene also had an identical twin, who shared the same DNA. Unable to determine which twin’s DNA was at the crime scene, investigators were unable to press charges.
You can still find the fingerprints of an ancient artisan on a clay pot made thousands of years ago, but you may not be able to detect the trace of a particular fingerprint left hours ago on an office door handle. That’s because how long a fingerprint lasts depends on what material it’s been left on, and what conditions that material experiences.
The forensic definition of fingerprints often refers to the traces of sweat and oil secreted from one’s skin that are left on hard surfaces. Known as latent prints, these traces of oil and sweat leave a mark in the form of the ridges of the finger that left it. Some materials like metal and glass hold these kinds of prints particularly well, due to their smooth and non-porous surface. Other elements such as humidity, rain, or even another person’s fingerprint, can erase the trace of a prior set of fingerprints.
Fingerprints can also be found on softer surfaces, formed in blood, dirt, paint, or soap. Known as patent prints, these types of fingerprints are formed when the patterned ridges of one’s fingertips make a direct impression on the surface that they touch. Patent fingerprints are generally longer lasting than latent fingerprints, but how long each lasts will still depend upon the surface material and outside conditions.
The ridges of skin that create a fingerprint run deep, and to remove them would require one to remove every layer of skin on their fingers. While some criminals have resorted to forms of self-mutilation in an attempt to erase their fingerprints, the patterns almost inevitably reform. In other cases, investigators are able to effectively reconstruct them.
The most famous case of attempted fingerprint removal was performed by John Dillinger, a notorious Depression Era criminal. Infamous for his bank robberies and prison escapes, his image was well known to the public, though he went to great lengths to obscure it. Dillinger resorted to plastic surgery to change his appearance and even attempted to burn off his fingertips with acid. He reportedly was unable to use his hands for days, but the procedure appeared to have worked—until he was shot dead by law enforcement, and forensic examiners saw that faint ridge marks had grown back just underneath the surface.
Fingerprints can be temporarily eroded, or even momentarily erased, unintentionally. Those who handle large volumes of paper, brick, or chemicals through the course of their work may have the ridges of their fingerprints eroded over time. Some chemotherapy patients have, through the side effects of treatment, seen their fingerprints fade away.
But no matter the motive or method of their erasure, fingerprints remain remarkably resilient and grow back.
Innovations are continuing to occur in fingerprint identification and pushing the boundaries of what a set of fingerprints can tell us. Researchers from Iowa State University recently published a study in Analytical Chemistry that proposed a way to determine not only who left a print where but also when they left it.
Others have found success in learning from the chemical traces left behind in fingerprints, including whether the person who left the print was a smoker or a user of a particular drug. As the craft of fingerprint identification continues to progress, fingerprints are telling a larger and larger story—and investigators are better learning to see it.
Matt Zbrog is a writer and freelancer who has been living abroad since 2016. His nonfiction has been published by Euromaidan Press, Cirrus Gallery, and Our Thursday. Both his writing and his experience abroad are shaped by seeking out alternative lifestyles and counterculture movements, especially in developing nations. You can follow his travels through Eastern Europe and Central Asia on Instagram at @weirdviewmirror. He’s recently finished his second novel, and is in no hurry to publish it.