The murder of a hairstylist in Chicago was part of a sexual fantasy hatched in an online chatroom between a former professor of an American university and a bursar of Oxford University, prosecutors said on Sunday (20 August).

Andrew Warren and Wyndham Lathem wanted to murder someone before killing themselves to realise a sexual fantasy they both shared.

Warren, who worked at Oxford's Somerville College, and Lathem, who was a teacher of microbiology at Northwestern University, were held without bail on Sunday after prosecutors made the gruesome allegations public for the first time.

Assistant State's Attorney Natosha Toller said the duo had chatted online for months about their dark fantasies before they executed it in late July.

Prosecutors said Lathem paid for Warren to visit the US and the two of them then decided to kill victims of Lathem's choosing. Their first target was Trenton Cornell-Duranleau, who also happened to be the US professor's boyfriend.

On the night of 26 July, Lathem lured Cornell-Duranleau to his apartment in the 500 block of North State Street and texted Warren that they would kill him that night, Toller said. Warren came around at 4.30am (9.30am GMT) in the morning after the 26-year-old hairstylist had fallen asleep.

Lathem stabbed the sleeping Cornell-Duranleau "over and over in the neck and chest area", while Warren kept watch at the doorway, Toller added.

When Cornell-Duranleau woke up and began to scream and fight back, Warren joined Lathem, putting his hands on the victim's mouth. He hit the young man in the head with a heavy metal lamp, prosecutors said.

Warren then left to get two kitchen knives and both men leaned over Cornell-Duranleau and continued stabbing him. The force of the stabbing was so much that Warren ended up breaking the blade of one of the knives he used, prosecutors added.

After the gruesome killing, the duo showered and left the apartment. They were arrested on 4 August separately after an eight-day manhunt.

While the pair were on the run, they reportedly donated $5,610 (£4,358) to the Howard Brown Health Center – an LGBT health and social services provider – and $1,000 to a public library in Lake Geneva in Cornell-Duranleau's name. Lathem also anonymously called the front desk of his apartment building to say that someone should check his room as a crime had been committed there.

He also sent a video message to his parents and friends, admitting to the killing and telling them "he is not the person people thought he was", prosecutors added.

Lathem was subsequently fired from Northwestern University and Warren suspended from his job.

Lathem's lawyer, Barry Sheppard, who spoke to reporters after the hearing, said that people should not "rush to judgment". He added that his client had led "a life of unblemished ... citizenship", which included academic work on the bubonic-plague virus.

The next hearing has been scheduled for Tuesday when another judge will join to supervise the case. Both Lathem and Warren will be given a chance to enter pleas at a later arraignment, the Chicago Tribune reported.