It’s a haunting, agonizing refrain in violent crimes that went unsolved for decades or were never solved at all: There were no fingerprints.

Then, Sir Alec John Jeffreys changed crime-solving forever.

Born January 9, 1950, the longtime genetics professor at the University of Leicester in England discovered in 1984 that patterns in some parts of a person’s DNA could be used to distinguish one person from another. The undisputed accuracy of “DNA fingerprinting” has had revolutionary impacts on the criminal justice system, as well as on the lives of victims’ families and the wrongly accused.

Jeffreys had already used his DNA pattern recognition technique in paternity and immigration cases—with well-publicized results—when police asked him to help solve cases involving the rape and murder of 15-year-old Dawn Ashworth in 1986 and a similar crime three years earlier.

Richard Buckland, a 17-year-old with learning disabilities, had confessed to the Ashworth murder. But when Jeffreys analyzed DNA samples from both crimes, he found they matched—and neither one matched Buckland’s genetic code.

After police collected blood and saliva samples from more than 4,000 men in the area, they found a match with Colin Pitchfork, a 27-year-old baker and father. He was arrested in 1987, convicted and sentenced to life in prison—where Buckland may have ended up were it not for Jeffreys’ discovery.

Years later, in an interview with the University of Leicester, Jeffreys admitted he first doubted the indicators from the DNA sample: “The police were sure they got the right guy (Buckland).” But more testing upheld his findings.

Jeffreys’ father and grandfather were prolific inventors. As a child, he was given a microscope and an “absolutely lethal” chemistry set—a reference to a sulfuric acid scar on his right cheek when an experiment went disastrously wrong. He covers it with a beard.

He earned a PhD from the University of Oxford in 1975, which introduced him to the world of genetics, and he spent two years at the University of Amsterdam working on trying to isolate genes before arriving at Leicester.

In 1984, he was working on the gene that codes for the protein myoglobin. Part of the gene consists of short sequences repeated many times. The number of repeats was found to vary between individuals.

At first, Jeffreys saw them as useful markers of the myoglobin gene. But eventually, he realized they were unique to the individual and could act as a fingerprint.

“The discovery of DNA fingerprinting was a glorious accident” while “messing about in the lab,” he said. The September 10, 1984 discovery was “a moment that changed my life.”

He said he figured DNA testing would be used as a last resort in criminal investigations but was happy to be “completely wrong.” The subsequent establishment of forensic DNA databases throughout the world underscores the science’s importance in solving crimes.

A 2005 inductee into the National Inventors Hall of Fame, Jeffreys has six patents. He is a recipient of the Lasker Award and the Royal Medal, and the Albert Einstein World Award of Science, among others.

With characteristic modesty, Jeffreys shuns the notion that DNA fingerprinting was one of the greatest discoveries of the 20th century. He said it was “good science and a lot of hard work.”

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