POLICE THOUGHT they knew who had written an online threat to carry out a massacre at a school when a local 18-year-old boy went missing with his grandfather's handgun on the day it was posted.
The teenager, from the town of Ottenburg, Baden-Wuerttemberg in Germany, seemed even more likely to be guilty when he was discovered two days later, dead in woods near his home from self-inflicted gunshot wounds.
But when officers examined the teenager's computer, they found no evidence linking him to the threat and realised that the person who wrote it must still be at large.
More than 3,700 police officers are involved in the hunt to find the real culprir. Three schools were placed on security alert while police guarded their buildings and carried out searches on pupils.
Although he was not the author of the threatening internet message, the dead boy was known to like violent computer games.
It was two secondary pupils playing such a game - Counter Strike - who notified their headteacher after they encountered a third person during an online chat threatening a bloodbath at their school on December 6.
The case echoes another shooting in Germany two weeks ago, when a disaffected 18-year-old opened fire on his school in the north-western town of Emsdetten, wounding 37 people before shooting himself. That teenager had a penchant for dressing in floor-length black clothes and also enjoyed violent computer games.
Politicians in Bavaria and Lower Saxony are now calling for a ban on so-called "killer games".
The Ottenburg incident has led to dozens of copycat internet threats by pupils in other areas of Germany, including Cologne and Frankfurt. One 19-year-old was arrested after sending an email to detectives in Baden-Wuerttemberg threatening to run amok at a vocational training school in Achern. He later admitted it was merely a ruse: he was trying to get his girlfriend "a day off".
Germany's worst school shooting happened at Gutenberg grammar school in Thuringia, in 2002. A 19-year-old who had been expelled killed 16 people then himself.
In 1999, at Columbine high school in Colorado, United States, 12 pupils and a teacher were killed.
At Dunblane primary in Scotland in 1996, Thomas Hamilton shot dead 16 pupils and a teacher before killing himself.