A 19-year-old man is being hunted on suspicion of murdering a nine-year-old boy in the western German town of Herne and boasting about the killing in an online video.
Police in the city of Bochum said authorities received a call late on Monday from a member of the public, who feared that a killing had taken place in the nearby town of Herne.
Officers searching the basement of a house found the body of the boy, said police spokesman Volker Schuette. The victim and the suspect were neighbours, he said.
A photo showing the suspect - named by police as Marcel Hesse - bragging about the killing was circulating on the so-called darknet, an area of cyberspace which is invisible on the open internet and used by some for illegal activity.
The photo has since appeared on regular social networking sites, Mr Schuette said.
Police warned that Hesse, who is unemployed and was previously unknown to police, could be armed and dangerous.
He was described as being thin, of average height, with short blond hair and glasses, and wearing clothes with a camouflage pattern.