A former Northwestern University professor and an Oxford University employee have pleaded not guilty to first-degree murder charges in the stabbing death of the professor’s boyfriend.

Wyndham Lathem, 46, and Andrew Warren, 56, stood quietly in separate Chicago court hearings on Thursday as their attorneys entered pleas on their behalf. Both men spoke little during the hearings, only briefly answering when Cook county judge Ursula Walowski asked if they understood the charges.

Unlike a previous court hearing, when prosecutors gave chilling details of the death of 26-year-old Trenton Cornell-Duranleau, Walowski simply laid out the charges. However, she referred to the crime as “exceptionally brutal” and said it was carried out in a “calculated and premeditated manner”.

The men are accused of attacking Cornell-Duranleau on 27 July while he slept in Lathem’s Chicago apartment, stabbing him dozens of times. Prosecutors are seeking a sentence of 20 years to life in state prison, Walowski said.

After Lathem’s hearing, his attorneys Barry Sheppard and Adam Sheppard said they would be filing a motion to have the two men tried separately, saying they did not want the jury to hear statements Warren made to police after he surrendered days later in San Francisco.

Barry Sheppard said Lathem made no statements to police when he turned himself in the same day in nearby Oakland. He said it was Warren’s statements that were the basis for the detailed account of the slaying that prosecutors read in court last month.

He said it would be impossible for Lathem to get a fair trial if a jury were to hear those words, either from Warren himself on the witness stand or from a testifying police officer.

In court, last month, prosecutors said that the fatal stabbing of Cornell-Duranleu was part of a sexual fantasy the two men hatched in an online chatroom, which included killing someone and then themselves.

Prosecutors alleged that Lathem had crept up to Cornell-Duranleau and began plunging a knife into his chest and neck, before Warren ran over to cover the victim’s mouth and strike him in the head with a heavy lamp in an attempt to silence him.

As Lathem continued stabbing Cornell-Duranleau, Warren left the room to retrieve two kitchen knives and returned to stab the victim as well, prosecutors said.

The two men then fled, triggering a nationwide manhunt that ended when the two men surrendered in California several days later.

Warren, a resident of Faringdon, Oxfordshire, has been suspended from his job as a senior treasury assistant at Somerville College, Oxford. Lathem, a microbiologist, was fired from his job at Northwestern University on 4 August.

Both men remain in Cook county jail, where they are being held without bail. Lathem is scheduled to return to court on 31 October. Warren’s next hearing is scheduled for 1 November.