Copenhagen (AFP) - A Danish submarine inventor being held over the grisly death of Swedish journalist Kim Wall is to appear in a Copenhagen court on Tuesday, where the suspicions against him could be ramped up to murder.

Peter Madsen is expected to appear in person at the court hearing due to begin at 2:00 pm (1200 GMT), the Danish public prosecutor's office told AFP.

The 46-year-old inventor has been been in custody since August 12 suspected of "negligent manslaughter" in a gruesome case that has puzzled investigators and shocked the public.

Danish prosecutors now plan to ask the Copenhagen district court to extend Madsen's detention, alleging that he murdered 30-year-old Wall and desecrated her body.

Wall's headless torso was found floating off Copenhagen on August 21, 10 days after she went missing while interviewing Madsen aboard his homemade submarine for a feature story she was researching about him.

Madsen has insisted that Wall died in an accident on board his 60-foot (18-metre) Nautilus submarine and that he later dumped her body at sea in Koge Bay near Copenhagen.

He denies cutting off her head and limbs, Danish police said.

But investigators say Wall's torso had been weighed down by a metal object, and her blood was found inside the submarine.

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"We will try to hold him in custody on a murder charge ... after her (dismembered) body was found," special prosecutor Jakob Buch-Jepsen told AFP on August 24.

Authorities are still searching for the rest of her remains, which they hope will provide some clues about the cause of death. Investigators have not commented on a possible motive.

The court is expected to ask Madsen to undergo a psychiatric evaluation.

- 'Search for clues' -

After Wall failed to return home following her interview on August 10, her boyfriend reported her as missing on August 11.

That same day, Madsen was rescued from waters between Denmark and Sweden shortly before his submarine sank.

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Investigators recovered and searched the vessel, which police believe Madsen sank intentionally.

After scanning the sub to rule out any hidden compartments and to "search for clues to the crime" on August 29, the police announced nothing new had been found.

Madsen is an eccentric self-taught engineer. In addition to launching his homemade submarine, he has also successfully launched rockets with the aim of developing private space travel.

The Nautilus was the biggest private sub ever made when Madsen built it in 2008 with help from a group of volunteers.

The volunteers were engaged in a dispute over the Nautilus between 2014 and 2015 before members of the board decided to transfer the vessel's ownership to Madsen, according to the sub's website.

- 'Cursed' -

In 2015, Madsen had 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 has spent his life attempting to break the boundaries of sea and space.

"My passion is finding ways to travel to worlds beyond the well-known," he wrote on the website of his Rocket Madsen Space Lab.

Danish police are still searching for the clothes Wall wore on the submarine: an orange fleece, a skirt and white sneakers.

Wall 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.

A graduate of the Columbia School of Journalism in New York, she had planned to move to Beijing to pursue her career.

Wall had written about the earthquake-hit ruins of Haiti, the macabre torture chambers of Idi Amin's Uganda, and Cubans using hard drives to access foreign culture.