Two significant clues were found in the children's ward that would prove helpful in catching the killer: footprints on the freshly cleaned floor and a water bottle that had been moved. Although there were several fingerprints on the bottle, police were able to account for all but one set. These prints also failed to match any of those in the police's database of known criminals.
Investigators fingerprinted over 2,000 people who had access to the hospital. Still, they couldn't find a match. Detective Inspector John Capstick then went even further: He decided that every man in the town of Blackburn, a city with more than 25,000 homes, would be fingerprinted.
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.
On August 11, police caught up with one of these men, Peter Griffiths. His footprints matched the ones found at the scene. When his fingerprints also came back a match, he confessed to the awful crime, blaming it on alcohol.
Griffiths was found guilty of murder and was executed on November 19, 1948.
Taken from: http://www.history.com/this-day-in-history [14.05.12]