Police said they were alerted Monday (Mar 6) by people who had viewed the clip on the Darknet, a hidden online arena notoriously used by criminals to trade weapons, drugs and child pornography.
A team of police discovered the child’s corpse around 19:30 GMT Monday in the basement of the suspect’s house in the town of Herne, North Rhine-Westphalia state.
The suspect was named as Marcel Hesse, described as an unemployed and socially withdrawn man not previously known to police.
Investigators said they could not rule out that he had also killed a woman.
Police in the western city of Bochum said he had in a conversation on the internet said that he had “fought a beast of 120 kilos” and that “she put up more of a fight than the child”.
Police said although the conversation could be bogus, they were taking it seriously “given the danger” Hesse posed.
Trained in martial arts, the 1.75 metre tall, slim, blonde man was thought to be wearing military style clothing and was possibly armed.
Police launched a large-scale search of the town Monday night, using sniffer dogs and helicopters.
“The victims and the suspect lived next door to each other,” said a police spokesman.
He added that authorities had no idea about a possible motive, saying that “there’s no one we can ask.”
Police did not report the content of the video.
Town Mayor Frank Dudda said, “We are bewildered and shocked, and we are mourning with the family.”