Submarine owner Peter Madsen stands inside the vessel. A Danish prosecutor said Madsen has been charged with murdering Swedish journalist Kim Wall during a trip on his private submarine. File picture: Niels Hougaard /Ritzau via AP

Copenhagen, Denmark - Inventor Peter Madsen was charged Tuesday with killing Swedish journalist Kim Wall during a trip on his private submarine, with prosecutors saying he either cut her throat or strangled her before dismembering her body and dumping it into the sea.

Prosecutor Jakob Buch-Jepsen called the case "very unusual and extremely disturbing."

Madsen, 47, is charged with murder, dismemberment and indecent handling of a corpse for the way he disposed of Wall's body. He is also charged with having sexual relations with Wall of "particularly dangerous nature."

The charges were made public by the Danish prosecution authority.

Buch-Jepsen said the killing was premeditated and prosecutors will urge that Madsen be sentenced to life in prison. Simultaneously, there is a secondary claim to put him in a secure mental facility if deemed necessary by psychiatrists for as long as he's considered sick and dangerous to others.

Read: Danish inventor admits dismembering journalist

Madsen and Wall had gone on a trip in Madsen's submarine on Aug. 10. Wall, who was working on a story about Madsen, was last seen aboard the vessel as it left Copenhagen. The next day, Madsen — an entrepreneur who once dreamed of launching a manned space mission — was rescued from the sinking submarine without Wall.

Police believe he deliberately sank the vessel.

Police technicians board Peter Madsen's submarine UC3 Nautilus on a pier in Copenhagen harbour, Denmark. File picture: Jacob Ehrbahn/Ritzau Foto via AP

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

Madsen has offered a shifting variety of explanations for Wall's death. Initially, he told authorities he had dropped Wall off on an island several hours after their voyage began. Then he claimed that Wall died accidentally inside the submarine while he was on deck during the excursion and he had "buried" her at sea. However, he later admitted throwing her body parts into the sea.

Wall's dismembered, naked torso was found on a southern Copenhagen shoreline in late August. Her head, legs and clothes were discovered in bags at sea in October, along with heavy metal objects designed to take them to the ocean floor.

Authorities also want to destroy Madsen's submarine.

Madsen's trial starts March 8 and a verdict is expected on April 25.

There was no immediate comment Tuesday from Madsen's defense lawyer, Bettina Hald Engmark.

AP