It was an unbelievably monstrous crime: a three-year-old who was in the hospital recovering from pneumonia was snatched from her bed in the middle of the night, sexually assaulted, and murdered. It appeared the girl had been held by her legs and swung skull-first into a wall until she died.

Who could have done such a heinous thing to tiny June Anne Devaney? Her injuries were so terrible the doctor who performed the post-mortem exam on her body speculated whoever’d done it was “in a state of maniacal frenzy.” Catching her killer was, understandably, a top priority for law enforcement.

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The date was May 14, 1948, so forensic science was still an emerging field. But police in Blackburn, England did have a very powerful weapon in their arsenal: fingerprinting. The attacker had left a series of footprints on the Queen’s Park Hospital floor, but more importantly, he’d also grasped a large bottle (see it in this short BBC clip) during his intrusion, leaving behind his own unique identifiers on the glass.

But once again, this was 1948—so the fingerprint database was relatively limited, June’s killer didn’t turn up among the existing local records. The mysterious prints also didn’t match any of people who worked at Queen’s Park Hospital. So in an unprecedented and massive effort, Blackburn police sent the prints to every cop shop in England—and they also ordered every male over the age of 16 who’d been in Blackburn when June was killed (some sources say over the age of 14) to have their fingerprints taken. It was “the first-ever mass fingerprint test,” according to the BBC.

As History.com recalls:

A procedure such as this would be impossible in the United States where Fourth Amendment protections prevent searches without probable cause. But the plan went into effect in Blackburn on May 23, with police assurances that the collected prints would be destroyed afterward. Two months later, the police had collected over 40,000 sets of prints yet still had not turned up a match. Checking against every registry they could find, authorities determined that there were still a few men in town who hadn’t provided their prints.

The investigation had gone on this long, and there was no stopping now. The remaining men were checked out—and once the entire adult male population of Blackburn had been printed, a match was found: Peter Griffiths, a 22-year-old former Guardsman. He was arrested on August 13, and once he found out his prints had been identified on the bottle from June Anne Devaney’s room, he confessed. (His footprints also matched, as did other forensic evidence gathered from the scene.)

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Griffiths was drunk at the time of the crime—that was his excuse. He was sentenced to death after just 23 minutes of jury deliberations, and met his end upon the gallows in November 1948.

Photo by Keystone/Hulton Archive/Getty Images