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 / Updated  / Source: Associated Press

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, 30, of a "particularly dangerous nature" before she was killed.

Swedish journalist Kim Wall.Courtesy Tom Wall / via AFP - Getty Images file

The charges were made public by the Danish prosecution authority.

Buch-Jepsen said the killing was premeditated. Prosecutors will urge that Madsen be sentenced to life in prison, or be locked up in a secure mental facility if deemed necessary by psychiatrists for as long as he's considered sick and dangerous to others.

Related: Submarine owner says Kim Wall buried at sea

"There is much technical evidence but I won't go into details right now," Buch-Jepsen told a brief news conference. He also declined to comment on Madsen's motive.

"Evidence must be presented in court and not in the media," he said, adding he also didn't want to comment out of respect for Wall's family.

FILE: This file photo taken on August 11, 2017 shows Peter Madsen (R), builder and captain of the private submarine "UC3 Nautilus" talking to a police officer in Dragoer Harbor south of Copenhagen, following a major rescue operation after the submarine sank in the sea outside Copenhagen Harbor.BAX LINDHARDT / AFP - Getty Images

Madsen's defense lawyer Betina Hald Engmark had no immediate comment in reaction to the charges, adding her client still denies murdering Wall.

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. 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.

Related: Danish inventor admits to dismembering journalist Kim Wall aboard submarine

Multiple knife wounds had been found on her torso and Buch-Jepsen said Tuesday Madsen had stabbed Wall several times while she was alive but declined to elaborate.

Authorities also want to destroy Madsen's submarine.

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

Special prosecutor Jakob Buch-Jepsen during a press briefing in front of the Copenhagen Police Headquarter, in Copenhagen, Denmark, 16 January 2018, after the prosecutor's office announced the charge in the submarine murder case against Peter Madsen.Jens Astrup / EPA