A Danish inventor has admitted dismembering a Swedish journalist who disappeared from his submarine, but says he did not kill her. Picture: Niels Hougaard /Ritzau via AP, File

Stockholm - Danish inventor Peter Madsen has admitted dismembering the corpse of Swedish journalist Kim Wall, whose body parts were found at sea after she interviewed him on board his homemade submarine, Danish police said Monday.

Madsen, who is suspected of murdering Wall, has until now denied mutilating her body.

In earlier police questioning, the 46-year-old said she had died in an accident when a heavy submarine hatch fell on her head, but he has now changed his story to say she died of carbon monoxide poisoning, police said in a statement.

"He has now explained that Kim Wall died as a result of carbon monoxide poisoning inside the submarine at a time when he was on deck," police said.

Read more: Submarine owner says missing woman died in accident

"Furthermore, Peter Madsen has admitted that he later dismembered her corpse and spread the body parts in Koge Bay" off Copenhagen.

Police also said Madsen was suspected of having "sexual relations other than intercourse ... under particularly aggravated circumstances, based on the 14 stab wounds to and around Kim Wall's genital area".

Read: Divers find missing body parts of Swedish journalist #KimWall

That was believed to have taken place shortly after her death, police said.  

Prosecutors have previously said they believe Madsen killed Wall as part of a sexual fantasy, then dismembered her body and tossed the parts into the sea.

Investigators found a hard disk in Madsen's workshop that contained fetish films in which women were tortured, decapitated and burned alive.

Madsen has denied any sexual relations with Wall, and insisted the hard drive did not belong to him.

Wall failed to return from an interview with Madsen on board his homemade submarine on August 10.

Also read: No sign of reporter who disappeared from submarine

Her headless torso was found floating in Koge Bay off Copenhagen on August 21, and her head, legs and clothes were recovered in plastic bags in the same waters on October 7.

Wall, 30, worked as a freelance journalist based in New York and China, and her articles were published in the Guardian, The New York Times and others.

Madsen, a 46-year-old self-taught engineer who is married, has been held in custody since August 11 and has changed his version of events several times.

After intentionally sinking his submarine early on August 11 in Koge Bay, some 50km from the Danish capital, he was picked up by a rescue vessel and told police he had dropped Wall off on land after their interview the previous evening.

Read more: Torso of journalist who vanished off submarine found in sea

On September 5, he changed his story to say a 70-kilo hatch fell on her head, killing her, and that he threw her body, intact, overboard in a panic.

But police said on October 7 they had located her decapitated head and an autopsy showed no sign of a skull injury.

The carbon monoxide poisoning explanation now "gives the police reason to request further information from the forensic coroner and the military's submarine experts," police inspector Jens Moller Jensen said in the statement.

Police said divers were still searching for Wall's arms, and both her and Madsen's cell phones.

Madsen is an eccentric, well-known figure in Denmark.

He has successfully launched rockets with the aim of developing private space travel.

And his homemade submarine Nautilus, launched in 2008, was the biggest private sub ever made when he built it with help from a group of volunteers.

A court hearing to extend Madsen's custody had been scheduled for Tuesday, but the hearing has been cancelled as he no longer contests his detention, police said.

Preliminary trial dates have been set for March and April, police said.

Under the Danish legal system, formal charges will be pressed against Madsen once the investigation has been completed, shortly before the trial.