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 / Updated  / Source: Associated Press

TALLINN, Estonia — A Danish inventor has admitted dismembering a Swedish journalist who disappeared from his home-made submarine in August and has changed his story about how she died, but still denies killing her, police investigating the bizarre case said Monday.

According to Copenhagen police, Peter Madsen now says Kim Wall died as result of carbon monoxide poisoning inside the submarine while he was on deck. Previously he had said she died after being accidentally hit by a heavy hatch in the submarine's tower.

"This explanation [by Madsen] naturally will lead the police into gathering additional statements from the coroner and the armed forces' submarine experts," said Copenhagen police investigator Jens Moller Jensen.

Police say Madsen acknowledged he dismembered her body and threw it into Koge Bay southwest of Copenhagen.

Related: Kim Wall Death: Danish Divers Find Missing Body Parts of Swedish Journalist

Wall's torso was found on a southern Copenhagen coast in late August, and her head, legs and clothes were found at sea this month. No fractures to Wall's skull were found that would have supported the claim that she was killed by the hatch.

Wall was working on a story about Madsen and was last seen aboard his home-made submarine Nautilus as it left Copenhagen in August.

Image: Kim Wall
Kim WallTOM WALL / AFP - Getty Images

The next day, Madsen was rescued from the sinking submarine without Wall. Police believe he deliberately sank the vessel.

Madsen's pre-trial detention is set to expire Tuesday but police said no new hearing will be held as the 46-year-old has voluntarily agreed to remain in detention.

Madsen is currently charged with murder and mutilating Wall's body. Police said Monday that the charges have now been extended to include sexual assault without intercourse. An examination of Wall's torso revealed wounds to her genitals and ribcage that were believed to have been caused during her death or shortly after.

Related: Headless Torso ID'd as Missing Submarine Journalist Kim Wall

"We're taking an approach that there exists a sexual motive," Jensen told Swedish broadcaster SVT.

Police have finished an unsuccessful search for the phones of Madsen and Wall in the past weeks but said they are mulling reactivating that search if needed.