Inventor Peter Madsen was formally charged with murdering Swedish journalist Kim Wall during a trip on his private submarine, a Danish prosecutor announced Tuesday, saying Madsen either cut Wall's throat or strangled her.

Prosecutor Jakob Buch-Jepsen said Tuesday the case is "very unusual and extremely gross," according to the Associated Press

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.

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.

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. Later, he said she had died in an accident on board and he had "buried" her at sea.

Madsen eventually admitted throwing her body parts into the sea. Her dismembered, naked torso was found on a southern Copenhagen coast in late August and her head, legs and clothes were discovered in bags at sea in October. Heavy metal objects were designed to take them to the ocean floor.

Authorities also want to destroy Madsen's submarine, the Associated Press reported.

The start of the trial has been set for March 8. A verdict is expected by April 25.

Buch-Jepsen said during a court hearing in October that investigators uncovered a hard drive from a computer Madsen owned containing video of the torture and killing of women.

"It's not just that we have the same grounds for arrest as before, but I think they are stronger than last time," Buch-Jepsen said, adding that Madsen should be detained during the hearing.

Madsen's body also had DNA traces from Wall, including scrapes on his face and neck, according to Buch-Jepsen.

Fox News’ Travis Fedschun and the Associated Press contributed to this report.