The Danish inventor accused of murdering journalist Kim Wall during a trip on his private submarine reportedly texted a former lover he had "a murder plan ready in the submarine" just days before the fatal voyage.

Peter Madsen, 47, planned Wall's murder last August by bringing a saw, screwdrivers, strips and pipes, which were used to hit, cut and stab the 30-year-old while she was alive, prosecutors said in an indictment last month.

Wall's cause of death has not yet officially been determined, but prosecutors said she died by either strangulation or the cutting of her throat. Prosecutor Jakob Buch-Jepsen said last month the case is "very unusual and extremely gross."

An unidentified woman who claims to be Madsen's former sexual partner said she'd "either seen or talked to Madsen nearly every day" before Wall's murder and recently told WIRED details of text messages the two shared that were "still bothering her."

Peter Madsen, right, the inventor charged with killing Kim Wall, left, had video of the torture and killing of women, a prosecutor said. (Reuters)

In one exchange in the days before Wall stepped onto Madsen's submarine Aug 10., the woman asked the inventor to "motivate her with a threat" to help her finish a project she was working on.

“He says he has a murder plan ready in the submarine, and I tell him 'I am not afraid, you have to be more threatening.' He talks about the tools he wants to use, and I say, ‘Oh it’s not threatening,’” the woman told WIRED.

KIM WALL 'TORTURED' BEFORE BEING KILLED ON HOMEMADE SUBMARINE, COPS SAY

The conversation soon "darkened," and Madsen discussed inviting someone to his homemade submarine, "where they would suddenly change the mood and begin cutting her up," according to the WIRED report.

The woman told the magazine she didn't give the text exchange much thought at the time, and it was "not something she took seriously." The unidentified woman has since turned the texts over to police.

Madsen 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 of a "particularly dangerous nature" with Wall.

The inventor 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.

KIM WALL MURDER: DANISH INVENTOR FORMALLY CHARGED IN 'UNUSUAL AND EXTREMELY GROSS' CASE

Madsen eventually admitted throwing her body parts into the sea, but denies murdering or sexually assaulting her. Wall's dismembered, naked torso was found on the southern Copenhagen coast in late August and her head, legs and clothes were discovered in bags at sea in October. Heavy metal objects were attached to make them sink to the ocean floor, according to prosecutors.

Peter Madsen, Danish inventor, engineer, rocket- and u-boat builder, talks about entrepreneurship during Danish Business Day event held in Copenhagen in May 2017. (Reuters)

The start of the Madsen's trial has been set for March 8 and a verdict is expected by April 25.

Wall's family and friends started to raise money in September for the "Kim Wall Memorial Fund Grant" as part of an online crowdfunding campaign that's raised more than more than $169,000 from donors around the world. The fund will award a female reporter a $5,000 grant on March 23, which would have been Wall’s 31st birthday.

The Associated Press contributed to this report.