June Anne had come into Queen's Park Hospital on 5 May to recover from a mild bout of pneumonia. By 14 May the worst was over and her bed in the children's ward was being made ready for someone else. The night nurse, Gwendolyn Humphreys, was in the kitchen preparing the children's breakfasts shortly after midnight when she heard a six-year-old boy in the ward begin to cry. She went in, soothed him back to sleep, and saw June Anne asleep in the next cot. It was the last time Humphreys would see her alive. At about 1:20 in the morning, Humphreys felt a draught from an open porch door, walked back to the ward, and found the cot empty. The drop-side was still up, which meant someone had lifted June Anne out. A trail of adult footprints in stockinged feet led across the highly waxed floor.

Staff searched for half an hour before calling the police, who arrived at 1:55 a.m. and began combing the hospital grounds. At 3:17 a.m. they found her, face down in the grass beside an eight-foot sandstone boundary wall, three hundred feet from the ward. The injuries told a story police did not want to tell her parents, and which a Wikipedia summary cannot tell with any grace either. She had been raped and killed by being swung against the wall. The chief constable of Blackburn telephoned Scotland Yard at 4:20 a.m. By 6:20 a.m., Detective Chief Inspector John Capstick and a sergeant were on the train north from Euston. June Anne's family, asleep when she was taken, were waiting at home for a small girl who had been told she could come home that day.

A Winchester bottle near the cot bore an unidentified set of prints. After eliminating all hospital staff and every tradesman, electrician, ambulance driver, and nurse's boyfriend who had been in the ward over the previous five years, one set remained. The head of the Lancashire Fingerprint Bureau declared it the murderer's. The ridges were sharp and unbroken, suggesting a young man who had not done years of hard labour. There was no match in any criminal record. DCI Capstick proposed something unprecedented: fingerprint every male aged sixteen and over who had been in Blackburn on the night of 14 to 15 May. The town then held 35,000 homes and 123,000 people. Officers promised the prints would be used only for this case and would be publicly destroyed afterwards. Inspector William Barton led a team of twenty officers through the districts, working from the electoral register, taking a left forefinger, middle, ring finger, and palm section on a custom card.

Two months of door-to-door work produced over 40,000 sets of prints and no match. By late July every name on the electoral register had been checked and eliminated. Then investigators turned to men who would not appear on the register: ex-servicemen recently discharged from the war that had ended only three years before, men who had moved to or from the town. Police cross-referenced the National Registration Numbers on recently issued ration books. Peter Griffiths, twenty-two years old, gave his prints without hesitation when asked. His niece had been a patient at Queen's Park Hospital on the night June Anne was taken. By the time his prints matched, officers had taken 46,253 sets and had fewer than 200 left to check. Griffiths confessed. At his trial, the defence argued he was in the early stages of schizophrenia. The jury rejected it. He was hanged at Walton Gaol on 19 November 1948.

Weeks before Griffiths was executed, the fingerprint cards collected from the men of Blackburn were taken to a local paper mill and pulped in front of invited journalists. The promise had been kept. The case is remembered now as the moment British policing learned that mass forensic investigation, conducted with public consent and clear limits, could solve crimes nothing else would solve. It is taught in police colleges and written up in textbooks of forensic science. But what changed in 1948 began with the loss of one small girl in a hospital cot, and the family who waited at home in Blackburn for a child who never came back. Queen's Park Hospital still stands, now part of the East Lancashire Hospitals NHS Trust. The sandstone wall is gone.