In 1948, the body of a 3-year-old pneumonia patient named June Anne Devaney was found on the grounds of Queen’s Park Hospital in Blackburn, England. She had been brutally murdered. Law enforcement officers were desperate to find her killer—so they took an unprecedented step to hunt him down.

The perpetrator had left a few clues—footprints on the children’s ward floor, blood, fibers, and fingerprints on a water bottle—but the prints didn’t belong to anyone in the police’s local database. Investigators collected prints from some 2000 people affiliated with the hospital, but they still couldn’t find a match.

Instead of declaring a cold case, detective inspector John Capstick took the investigation a step further: He decided that every single man over the age of 16 (though some accounts say 14) who’d been in the town of Blackburn during June’s killing would be fingerprinted. Capstick also made sure that the prints found at the murder site were sent to all police fingerprint bureaus in the United Kingdom. According to the BBC and Cheryl Eddy of io9's True Crime, the ambitious endeavor was “the first-ever mass fingerprint test”—athough Capstick did promise Blackburn’s mayor that the prints would be destroyed after the crime was solved. 

More than two months and over 40,000 sets of prints later, the murderer still hadn’t been found—but population records revealed that 200 people hadn’t provided their marks. Once the police collected the remaining individuals' fingerprints, they spotted a match.

Peter Griffiths—a 22-year-old former military serviceman—was arrested, and confessed to the killing after being told that his prints had been found on the water bottle. A trial was later held, and it took a judge only 25 minutes to find Griffiths guilty and sentence him to death. 

This was the first timebut not the lastthat the British police would take similar forensic measures. In 1954, the Metropolitan Police took the palm prints of 10,000 men after a woman was murdered on a golf course. Although they, too, ended up catching the killer, the practice of mass fingerprinting grew controversial with time. 

In 1976, people protested when police wanted to collect fingerprints from 15,000 people—including youths over the age of 12—when an elderly lady was murdered in Newcastle-Upon-Tyne. Although officials assured the public that parental consent would be requested and the prints would be destroyed, the National Council for Civil Liberties expressed concern. The practice, they said, brought "nearer the day when the public would be asked to accept such blanket police techniques as unavoidable, and was a very serious step on the path to a system of universal databank holding information on individuals which was in the hands of the police or government."

Mass fingerprinting endeavors have continued in England up to recent times. In 2002, more than 1258 sets of prints were collected from residents of England's Norfolk Island after the population experienced its first murder in 150 years. News articles also show that mass fingerprinting has been used to help solve crimes in America—although the practice has incited criticism from the American Civil Liberties Union.

The Fourth Amendment limits the use of fingerprinting, and it's likely Americans wouldn't be as willing to provide their prints as Blackburn's men were more than 70 years ago. Meanwhile, the practice remains controversial in England, where citizens oppose biometric passport programs and the fingerprinting of children in schools. Nevertheless, the investigation of June Anne Devaney's murder was still an important—and fascinating—chapter in the history of forensic science.

[h/t io9