In May 2004, agents from the Federal Bureau of Investigation showed up at Brandon Mayfield's law office and arrested him in connection with the March 2004 bombing of a train station in Madrid, Spain. The Oregon lawyer was a suspect because several experts had matched one of his fingerprints to a print found near the scene of the terrorist attack.
But Mayfield was innocent. When the truth emerged 2 weeks later, he was released from jail. Still, Mayfield had suffered unnecessarily, and he's not alone.
Police often use fingerprints to nab criminals.
Police officers often use fingerprints successfully to nab criminals. However, according to a recent study by criminologist Simon Cole of the University of California, Irvine, authorities may make as many as 1,000 incorrect fingerprint matches each year in the United States.
"The cost of a wrong decision is very high," says Anil K. Jain, a computer scientist at Michigan State University in East Lansing.
Jain is one of a number of researchers around the world who are trying to develop improved computer systems for making accurate fingerprint matches. These scientists sometimes even engage in competitions in which they test their fingerprint-verification software to see which approach works best.
The work is important because fingerprints have a role not just in crime solving but also in everyday life. A fingerprint scan may someday be your ticket to getting into a building, logging on to a computer, withdrawing money from an ATM, or getting your lunch at school.
Everyone's fingerprints are different, and we leave marks on everything we touch. This makes fingerprints useful for identifying individuals.
Everyone's fingerprints are different.
People recognized the uniqueness of fingerprints as far back as 1,000 years ago, says Jim Wayman. He's director of the biometric-identification research program at San Jose State University in California.
It wasn't until the late 1800s, however, that police in Great Britain started using fingerprints to help solve crimes. In the United States, the FBI began collecting prints in the 1920s.
In those early days, police officers or agents coated a person's fingers with ink. Using gentle pressure, they then rolled the inked fingers on a paper card. The FBI organized the prints on the basis of patterns of lines, called ridges. They stored the cards in filing cabinets.
In the fingers and thumbs, ridges and valleys generally form three types of patterns: loops (left), whorls (middle), and arches (right).
Today, computers play an important role in storing fingerprint records. Many people getting fingerprinted simply press their fingers on electronic sensors that scan their fingertips and create digital images, which are stored in a database.
The FBI's computer system now holds about 600 million images, Wayman says. The records include the fingerprints of anyone who immigrates to the United States, works for the government, or gets arrested.
Looking for a match
TV series such as CSI: Crime Scene Investigation often show computers searching for matches between FBI records and fingerprints found at crime scenes.
To make such searches possible, the FBI has developed the Integrated Automated Fingerprint Identification System. For each search, computers run through millions of possibilities and spit out the 20 records that most closely match a crime-scene print. Forensics experts make the final call on which print is the most likely match.
The Integrated Automated Fingerprint Identification System allows law enforcement officials to look for fingerprint matches.
Despite these advances, fingerprinting is not an exact science. Prints left at a crime scene are often incomplete or smeared. And our fingerprints are always changing in slight ways. "Sometimes they're wet, sometimes dry, sometimes damaged," Wayman says.
The process of taking a fingerprint can itself change the print that's recorded, he adds. For example, the skin may shift or roll when a print is taken, or the amount of pressure may vary. Each time, the resulting fingerprint is a little bit different.
Computer scientists have to be careful when they write programs to analyze prints. If a program requires too exact a match, it won't find any possibilities. If it looks too broadly, it will produce too many choices. To keep these requirements in balance, programmers are constantly refining their techniques for sorting and matching patterns.
Researchers are also trying to find better ways to collect fingerprints. One idea is to invent a scanner that would allow you to simply hold your finger in the air, without putting pressure on a surface.
Further improvements are necessary because, as Mayfield's case demonstrates, things can go wrong. The FBI did find several similarities between Mayfield's fingerprint and the crime-scene print, but the print found at the bomb site turned out to belong to someone else. In this case, the FBI experts initially jumped to the wrong conclusion.
Fingerprint scans aren't just for solving crimes. They can also play a role in controlling access to buildings, computers, or information.
Fingerprints aren't just for solving crimes.
At the door of Jain's lab at Michigan State, for example, researchers enter an ID number into a keypad and swipe their fingers across a scanner to enter. No key or password is required.
At Walt Disney World, admission passes now include fingerprint scans that identify holders of annual or seasonal tickets. Some grocery stores are experimenting with fingerprint scanners to make it easier and faster for customers to pay for groceries. Fingerprint readers at certain ATMs control cash withdrawals, foiling criminals who might try using a stolen card and pin number.
Schools are starting to use finger-identification technology to speed students through lunch lines and to track library books. One school system has installed an electronic-fingerprint system to keep tabs on students riding on school buses.
The number of potential applications of fingerprint scans for identifying people is huge, but privacy is a concern. The more information that stores, banks, and governments collect about us, the easier it may be for them to track what we are doing. That makes many people uncomfortable.
Your fingerprint says a lot about you. Every time you use your hands, you leave a little bit of yourself behind.