A Danish court has ordered the owner of a home-made submarine which sank off Copenhagen to be detained for 24 days while police investigate the disappearance of a Swedish journalist who had been on board.

Peter Madsen was arrested on Friday on preliminary manslaughter charges over the disappearance of 30-year-old Kim Wall after his 40-tonne, 60ft-long submarine sank off Denmark’s eastern coast.

Madsen has denied responsibility for the fate of Ms Wall, saying she had disembarked before his vessel went down.

Swedish journalist Kim Wall had been on the submarine (Tom Wall/AP)
Swedish journalist Kim Wall had been on the submarine (Tom Wall/AP)

Judge Kari Soerensen announced the ruling after a two-hour custody hearing held behind closed doors.

Madsen’s defence lawyer, Bettina Hald Engmark, said her client maintains he is innocent.

Ms Hald Engmark said Madsen is “willing to cooperate” and has not decided whether to appeal the detention ruling.

Before the hearing was closed, the courtroom was packed with Danish and Swedish reporters and the 46-year-old Madsen’s relatives.

Danish maritime authorities work on a salvage operation, taking place in connection with a criminal investigation
Danish maritime authorities work on a salvage operation, taking place in connection with a criminal investigation (Brian Linberg Jensen/AP)

Prosecutor Louise Pedersen said Madsen faces the preliminary manslaughter charge “for having killed in an unknown way and in an unknown place Kim Isabell Frerika Wall, of Sweden, sometime after Thursday, 5pm.”

Ms Wall’s boyfriend alerted authorities early Friday that the sub had not returned to Copenhagen as expected, prompting a major search involving two helicopters, three ships and several private boats.

The Navy said the sub, the UC3 Nautilus, was seen sailing, but then sank shortly afterwards.

Kristian Isbak, who had responded to the Navy’s call to help locate the ship on Friday, said he first spotted Madsen standing wearing his trademark military fatigues in the submarine’s tower while it was still afloat.

He then climbed down inside the submarine and there was then some kind of air flow coming up and the submarine started to sink,” Mr Isbak said. “(He) came up again and stayed in the tower until water came into it”, before swimming to a nearby boat as the submarine sank.

The owner of the sunken submarine has been detained pending missing journalist probe
The owner of the sunken submarine has been detained (Brian Linberg Jensen/AP)

Madsen told authorities he had dropped Wall off on an island in Copenhagen’s harbour a few hours into their Thursday night trip.

“It is with great dismay that we received the news that Kim went missing during an assignment in Denmark,” her family said.

The Sweden-born freelance journalist studied at the Sorbonne university in Paris, the London School of Economics and at Columbia University in New York, where she graduated with a master’s degree in journalism in 2013.

She lived in New York and Peking, her family said, and had written for The New York Times, The Guardian, the South China Morning Post and Vice Magazine, among other publications.

A salvage vessel, the Vina, raised the submarine on Saturday. The vessel was 23ft underwater off Copenhagen’s south island of Dragoer. The submarine was brought up some 4.3 miles off the coast and is expected to be transported to land at some point.

In theory, the Nautilus can dive up to 1,550ft but has rarely gone deeper than 132ft, according to Madsen’s business web site.

If tried and found guilty, Madsen faces between five years and life in prison.