A Danish inventor charged with murdering Swedish journalist Kim Wall tied up and tortured her before killing her, prosecutors allege.

Peter Madsen, 46, is accused of using a special tool kit to brutalise Wall on board his home-made submarine before either strangling her or slitting her throat in August last year.

He then dismembered her body, wrapped the parts in plastic bags and dumped them into Copenhagen harbour before scuttling his sub, the UC3 Nautilus.

Kim Wall was on Madsen's submarine as research for an article when she went missing.
Kim Wall was on Madsen's submarine as research for an article when she went missing.

Madsen admits abusing her corpse but maintains Wall died by accident after a hatch fell on her head while she was on board.

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She had agreed to ride along with Madsen on his submarine for a story she was writing.

The charges were revealed on January 16 but without any additional details. A copy of the charge sheet has since been obtained by the Associated Press.

Madsen's trial will begin on March 8, when he will be charged with premeditated murder as well as dismemberment and "sexual relations other than intercourse of a particularly dangerous nature". Lawyers will be seeking a life term.

Supporters of the inventor have vandalised his submarine which is being held near Copenhagen harbour, Swedish newspaper Afton Bladet reports.

Police technicians board Peter Madsen's submarine UC3 Nautilus on a pier in Copenhagen harbour, Denmark on August 13, 2017. Photo / AP
Police technicians board Peter Madsen's submarine UC3 Nautilus on a pier in Copenhagen harbour, Denmark on August 13, 2017. Photo / AP

Vandals used spray paint to write "Free Madsen" down the side of the craft, along with the word "Uskyldig" - which means 'innocent' in Danish.

Prosecutor Jakob Buch-Jepsen said the case is "very unusual and extremely brutal".

Wall was last seen on August 10 boarding Madsen's submarine for a trip around Copenhagen harbour.

In the early hours of the following morning Madsen called the coastguard to report the craft was sinking, after which it became apparent Wall was missing.

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Madsen initially denied any knowledge of her fate, saying he dropped her off on shore before the submarine ran into trouble.

But he later changed his account, saying she was killed by accident after a heavy hatch fell on her head.

One of the final photos of Kim Wall, with Peter Madsen as they depart on UC3 Nautilus.
One of the final photos of Kim Wall, with Peter Madsen as they depart on UC3 Nautilus.

Divers were quickly able to recover the wreck of the Nautilus from the bottom of the harbour, but found no trace of Wall on board except for her underwear.

Her torso was discovered almost two weeks after she was last seen, before her head and legs were discovered in October.

Crucially, examiners said the skull bore no evidence of a fracture which would corroborate Madsen's account.

Two arms were then discovered in the same area in November. All the body parts had been weighted down with metal.

Police also found some of Wall's clothes and a knife in one of the bags.

Earlier, prosecutor Jakob Buch-Jepsen told a court custody hearing that a hard disk found in Madsen's workshop contained fetish films in which real women were tortured, decapitated and burned.

Copenhagen Police's Special prosecutor Jakob Buch-Jepsen speaks to the press on January 16 after Madsen was charged with killing Wall. Photo / AP
Copenhagen Police's Special prosecutor Jakob Buch-Jepsen speaks to the press on January 16 after Madsen was charged with killing Wall. Photo / AP

Madsen, who is married, denied the hard drive belonged to him and has denied any sexual relationship between himself and Wall.

Prosecutors have previously said they believe Madsen killed Wall as part of a sexual fantasy, and found multiple mutilation wounds to her genitals.

Madsen is a self-taught engineer has successfully launched rockets with the aim of developing private space travel.

He is known for his occasionally foul temper and fallouts with former colleagues.

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.

Madsen claimed in an email to people who had helped build Nautilus that the vessel was cursed. Photo / Getty
Madsen claimed in an email to people who had helped build Nautilus that the vessel was cursed. Photo / Getty

But they became engaged in a long-running dispute over the Nautilus, before members of the board decided to transfer the vessel's ownership to Madsen, according to the sub's website.

In 2015, Madsen sent a text message to two members of the board claiming: "There is a curse on Nautilus".

"That curse is me. There will never be peace on Nautilus as long as I exist," Madsen wrote, according to the volunteers.

Madsen's character is expected to be central to the murder case against him. A verdict is expected on April 25.