CHICAGO (CBS) — A University of Oxford treasury assistant charged for his role in the gruesome stabbing death of a 26-year-old hair stylist last month has agreed to return to Chicago, a week after he turned himself in to authorities in San Francisco.

Andrew Warren, 56, appeared before a judge in San Francisco Superior Court on Friday and waived extradition to Chicago. Warren and former Northwestern University associate professor Wyndham Lathem fled Chicago after Trenton James Cornell-Duranleau was found stabbed to death in Lathem’s apartment on July 27.

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Police identified Lathem and Warren as the alleged killers days after Cornell-Duranleau’s body was found, and issued first-degree murder warrants for their arrests.

Warren — a senior treasury assistant at Somerville College, a part of the University of Oxford in Great Britain — surrendered to police in San Francisco last week. Lathem, 42, surrendered to federal authorities in Oakland.

Lathem made his first court appearance in California on Monday, and waived extradition. Lathem was an associate professor of microbiology and immunology at Northwestern, but was fired after he was taken into custody.

On Thursday KPIX 5’s Juliette Goodrich spoke face-to-face with Lathem, who appeared calm. Cameras were not allowed.

KPIX 5: Did you have anything to do with the killing of Trenton Cornell Duranleau ?

LATHEM: I know you have come all this way to talk to me and I am sorry. I have been advised by my attorney not to say anything without him.

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KPIX: Why did you send a video to family and friends apologizing for your involvement in the crime, saying “it was the biggest mistake of my life” ?

LATHEM: I’m sorry I can’t talk unless my attorney says I can.

It was not immediately clear when Warren and Lathem would return to Chicago to face charges.

Chicago police have not said what role each man allegedly played in Cornell-Duranleau’s death, but have said he and Lathem had a relationship.

Police said Cornell-Duranleau was stabbed more than 40 times. CPD spokesman Anthony Guglielmi said the attack on the victim “certainly was very intense,” and believe there might have been some tension in Lathem and Cornell-Duranleau’s relationship.

Guglielmi has said officers found a “very gruesome” crime scene inside Lathem’s apartment in the River North neighborhood, adding the victim was “savagely murdered.”

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Lathem and Warren allegedly travelled to Lake Geneva, Wisconsin, after the murder and made a $1,000 donation to the Lake Geneva Public Library in the victim’s name, Chicago police said. Lathem also allegedly sent an apologetic video to friends and family members.