The Danish inventor accused of killing Swedish journalist Kim Wall aboard his private submarine last summer may now face life in prison.

Prosecutors have now charged Peter Madsen with murder and sexual assault, over an original charge of involuntary manslaughter.

And, they say, he either strangled the 30-year-old woman or cut her throat.

Madsen denies both charges.

Wall was last seen alive when she embarked with Madsen aboard his submarine from Copenhagen in August. She was interviewing the entrepreneur obsessed with do-it-yourself engineering.

Reuters profiled one of his endeavors, these space rockets, five years ago.

The first days after Wall's disappearance brought conflicting accounts from Madsen. First he said he dropped her off on shore before his sub sank in a sea disaster. Then he said she died in a freak accident and he buried her at sea.

But authorities say Madsen appears to have deliberately scuttled the watercraft and attempted to hide Wall's body by dismembering it and weighing it down on the ocean floor.