Peter Madsen, the Danish inventor who brutally murdered a journalist in his homemade submarine, briefly escaped from prison Tuesday by taking a prison psychologist hostage.

The 49-year-old was able to escape Herstedvester Prison in the western suburbs of Copenhagen, where he is serving a life sentence for the 2017 murder of journalist Kim Wall, by threatening the female psychologist with a “gun-like object”, according to local media reports.

Madsen was arrested a short time later, about a kilometre away, with Danish police confirming a man had been arrested after an attempted escape and that the area had been cordoned off.

Footage from the scene showed Madsen sitting in grass by the roadside, with what appeared to be a belt around his waist, surrounded by armed police and dog units. Danish newspaper Ekstra Bladet reported that there were unconfirmed reports that Madsen had also claimed to have a bomb.

According to authorities, guards immediately sounded an alarm and chased the killer, but then had to withdraw when he threatened them, allowing him to walk through the prison’s gates. Prison official Bo Yde Sørensen told the Ekstra Bladet that he supported the guards’ decision to let Madsen leave the prison, as they had assessed there was a potential danger to the hostage’s life.

Madsen already had a public profile as an eccentric inventor and entrepreneur when he became one of Denmark’s most reviled men following the August, 2017 murder of Wall, a 30-year-old Swedish freelance journalist.

Wall had disappeared after meeting Madsen for an interview on his homemade submarine. Madsen initially claimed he had dropped her off safely on shore, but later admitted dismembering her and discarding her body overboard. He was found guilty of her murder in 2018.