German police on Thursday arrested a 19-year-old man suspected of stabbing a nine-year-old boy to death and bragging about the murder in an online video -- and discovered another body.

The man, named as Marcel Hesse, was arrested after he went into a restaurant in the northern town of Herne Thursday night and shouted: "Call the police, I'm wanted", Bild newspaper reported.

Authorities had been hunting for Hesse for several days after they were alerted 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corpse on Monday when they searched the cellar of the suspect, who has been described as an unemployed and socially withdrawn man not previously known to authorities.

The child had been Hesse's neighbor and investigators Monday said they could not rule out that he had also killed a woman.

After his arrest Thursday night, Hesse put the investigators on the trail of an apartment he had just burned and in which a second dead body was found.

In a conversation on the internet Hesse had said that he had "fought a beast of 120 kilos" (260 pounds) and that "she put up more of a fight than the child."

After his arrest, Marcel H was taken to nearby Bochum police station, before being examined by a doctor.

The child's family told dpa through their lawyer Reinhard Peters that they were "relieved" about Marcel's arrest and that it had helped them come to terms with what had happened.

"The question of why is of the utmost importance," Peters added. "They want to understand what happened."

The lawyer said that Marcel had lured 9-year-old Jaden to him by asking him to hold a ladder for him. The boy's brother had overheard the conversation.

A 34-year-old woman who lives in the building where the fire took place said she was, "sad that he (Marcel H) managed not to be caught for three days."

"You're afraid for your own children," another woman from the neighborhood added. "He's destroyed the lives of the parents. It's sick what he did."

Police are to give a press conference with further details about the case on Friday afternoon. A memorial for Jaden is planned for next Thursday.