The TV show Case Number XY (Aktenzeichen XY) was an immediate hit when it went on the air on Germany's second public broadcasting station, ZDF, in 1967.

From the moment of its first, sonorous opening proclamation -- "Ladies and Gentlemen, using the screen as a crime fighting device is the object of our TV series Case Number XY," -- viewers did all they could to help solve the crime featured each week.

The untimely death of Dr. Boll

The premise was a good one, and results were almost immediate: twelve hours after the sixth show, the murder of a certain Dr. Boll was solved. It can even be argued that the show changed the face of television, spawning an array of real-crime programs across Europe and the US.

Whatever its effect on the viewing public, Case Number XY certainly has affected the lives of a number of lawbreakers. The show's producers say 42 percent of the "unsolveable" crimes they featured were, indeed solved.

Help for desperate detectives

So detectives in Cologne must have been thrilled to find out that the popular program would feature -- on its anniversary broadcast, no less -- a murder case that they had been fruitlessly pursuing since October, 2006. In their search for a man who had given a 20- year-old prostitute knockout drops, then robbed and killed her in a fleabag hotel, the trail had gone cold.

They didn't know where else to turn for help.

Fortunately for the Cologne cops, some civil servants in Munich watched the show. Thanks to Case Number XY, two justice officials and policemen recognized the missing assailant. He had been convicted of drug smuggling in Munich, and was doing time in a prison there.