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The July slaying of a man allegedly at the hands of two university staffers was part of a twisted sexual fantasy that began online, prosecutors said Sunday.

Wyndham Lathem, an associate professor and microbiologist at Northwestern University, in Illinois, and Andrew Warren, a financial officer at Oxford University, in England, have been charged with first degree murder in connection with the fatal stabbing of Lathem’s boyfriend, authorized said.

An Illinois prosecutor said during a bond hearing Sunday afternoon that the two had met on the internet and made a plan online to kill someone and then to kill themselves. The plan was allegedly hatched months before Lathem paid for Warren to come from England to Chicago in July, prosecutors said.

Earlier Sunday, Chicago authorities first revealed that they believed the motive for the grisly murder was “not domestic in nature,” but something “more dark and disturbing."

Trenton James Cornell-Duranleau via Facebook

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The body of 26-year-old Trenton Cornell-Duranleau was found in Lathem’s apartment on July 27 after an anonymous phone call was placed to the building’s doorman that he should investigate the residence for a possible crime, police said.

Police said they now believe Lathem, who was in a romantic relationship with the victim, himself placed that call.

“What they discovered in that apartment can only be described as savage and grisly and shocked what is otherwise a very safe area,” Chicago Police Superintendent Eddie Johnson said at a press conference Sunday.

Cornell-Duranleau was brutally stabbed to death, authorities said — in an attack that was so violent one of the blades found in the apartment was broken.

Wyndham Lathem on Aug. 19. Chicago Police Department / via AP

Witnesses allegedly heard “what sounded like a fight and screaming” at around 5 a.m. the morning authorities believe the murder took place, said Brendan Deenihan, commander of Area Central Detectives.

According to prosecutors, the victim’s last words to his boyfriend and alleged killer were, "Wyndham, what are you doing?" NBC Chicago reported.

Lathem, 42, and Warren, 56, were apprehended after an eight-day manhunt following the call the door man, police said. The two were tracked down to California and authorities negotiated with the suspects’ lawyers to get both men to turn themselves in on Aug. 4.

Andrew Warren on Aug. 19. Chicago Police Department / via AP

Deenihan said at the press conference that they didn't believe the motive behind the killing “was domestic in nature," but left the details to the prosecutors.

“What I can tell is it was not domestic in nature ... that was not the motive, it was a little bit more dark and disturbing as far as I’m concerned,” he said.

It's also alleged that Lathem and Warren made a $1,000 donation to a library in Wisconsin in Cornell-Duranleau’s name before fleeing to California.

The pair was extradited to Illinois on Friday and both men have been charged with first-degree murder. A judge on Sunday ordered them held without bail.