Both men are charged with first-degree murder in the stabbing death of Lathem's boyfriend, 26-year-old Trenton James Cornell-Duranleau.
But their alleged motive for the brutal stabbing of Cornell-Duranleau, a hairstylist who had just moved to Chicago from MI, remained a mystery.
He was terminated by the university for fleeing from police while an arrest warrant was out for him.
Superintendent Eddie Johnson said Lathem had not "entirely acted alone and was joined by" Warren in the attack.
They surrendered separately to authorities in California earlier this month. 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.
Cornell-Duranleau was stabbed 70 times, and with such force that his head was almost decapitated.
Lathem was an associate professor at Chicago's prestigious Northwestern University and specialises in research surrounding the Black Death, but has since been sacked.More news: All Blacks humble Wallabies again
The Daily Northwestern cited The Chicago Tribune in reporting that autopsy results revealed that Cornell-Duranleau, a 26-year-old hairstylist, had methamphetamine in his system at the time of the murder. According to prosecutors, who cited the findings of the Cook County Medical Examiner's Office, Cornell-Duranleau had been stabbed 70 times, WMAQ reported.
As prosecutors laid out the case against Warren and Lathem, a former Northwestern University professor, they said it was premeditated murder.
Lathem called to Warren for help in controlling Cornell-Duranleau, authorities allege, at which point Warren placed his hand over the victim's mouth, then struck him in the head with a heavy metal lamp.
The commander said: "It was not domestic in nature like a husband-wife, or boyfriend-boyfriend, or love triangle - that was not the motive".
Cornell-Duranleau's death occurred the same day one of the suspects walked into the public library of Lake Geneva, a Wisconsin resort city about an hour's drive from Chicago, and made a $1,000 cash donation in the victim's name. "It was a little bit more dark and disturbing as far as I'm concerned".
Lathem also sent a video to friends and relatives apologising for his involvement in the crime, which he described as the "biggest mistake of my life". Lathem was taken into custody by U.S. Marshals in Oakland, Calif., on August 4.
Lathem's attorney, Adam Sheppard, told the Chicago Sun-Times that the former professor was expected back in Chicago Friday night.