An undated mug shot shows Wyndham Lathem. (Chicago Police Department)

Cook County prosecutors and defense attorneys for Wyndham Lathem, a former Northwestern University professor and microbiologist, offered differing theories for how his boyfriend ended up dead and nearly decapitated inside Lathem’s River North apartment four years ago.

Monday marked the first day of Lathem’s murder trial, after he and another man allegedly stabbed 26-year-old Trenton Cornell-Duranleau 78 times.

During opening statements, Cook County prosecutors painted Lathem as a wealthy, powerful professional who took advantage of a young man just trying to make his way in Chicago.

“This defendant may have shown one face to the world — respectable, prestigious doctor,”  Assistant State’s Attorney Matthew Thrun said. “But Trenton saw another face.”

Prosecutors alleged Lathem and Andrew Warren carried out a “sexual fantasy” in killing Cornell-Duranleau, stating the pair had been communicating through an online chatroom for months before the killing.

But Thrun said the evidence is “clear and overwhelming” that it was Lathem who took the lead in orchestrating the killing.

Warren pleaded guilty to his role in the killing in 2019. He’s expected to be one of the key witnesses against Lathem at trial, and received a 45-year prison sentence recommendation in exchange for his testimony.

Lathem’s attorneys pointed the finger back at Warren, claiming he’s a serial liar who is only testifying because prosecutors may allow him to serve his sentence in his home country of England.

According to prosecutors, Lathem had been dating Cornell-Duranleau, who did not have a full-time residence, and lured him to his River North apartment the night before the killing.

Thrun said Lathem could be seen letting Warren into his apartment at around 4 a.m. the next morning, and there was a noise complaint shortly after by another resident who heard someone shouting for help.

Police later found Cornell-Duranleau lying dead on the floor of Lathem’s home, having been nearly decapitated during the attack.

READ: Criminologist: Suspects in Stabbing Case Don’t Match Typical Profile

Lathem and Warren then allegedly fled Chicago following the killing and eluded capture for more than a week as they made their way out west.

During that time, Lathem made a stop to record a video expressing his remorse for their crime, calling it the “biggest mistake of his life,” according to police, and made a donation in Cornell-Duranleau’s name to the Lake Geneva Public Library in Wisconsin.

The two eventually turned themselves in to authorities in California several days after they “ran out of road” to run, prosecutors said.

But Lathem’s attorneys said the killing had started out as a sexual encounter between the three men that went wrong. Defense attorney Kenneth Wine said the three men were together in bed, but at some point Cornell-Duranleau began hitting Lathem. They claimed Lathem ran to the bathroom in shock, and when he returned, Warren had used two knives to stab Cornell-Duranleau and hit him over the head with a lamp.

Wine argued Lathem had no motive to kill and was “overcome with grief” at the death of his lover, and that Lathem himself wanted to die afterwards. He is expected to take the witness stand and testify in his own defense at trial.

Wine also claimed Warren changed his story just last week, allegedly telling prosecutors he was “sure that what (he’d) done” had killed Cornell-Duranleau.

Though most of the jurors had no prior knowledge of this case, the brutal 2017 slaying and the subsequent manhunt for Lathem and his alleged accomplice Andrew Warren made headlines around the world.

The trial is expected to take about two weeks and could include testimony from close to 50 witnesses.

Contact Matt Masterson: @ByMattMasterson | (773) 509-5431 | [email protected]