He is charged alongside Wyndham Lathem, former professor of Northwestern University in Chicago.
Lathem then paid for Warren to stay in a hotel near his 10th-floor condo. According to Toller, the men used a rented auto to travel - making a $5,610 donation in Cornell-Duranleau's name to a health center a $1,000 donation in Cornell-Duranleau's name to the Geneva public library.
Both donations were made in the name of his dead boyfriend, "Cornell-Duranleau".
Lathem turned himself in to police in Oakland, California, on August 4 and agreed to be extradited back to Chicago where he is expected to plead not guilty to the murder charge, his attorney, Adam Sheppard, previously told PEOPLE.
Both men allegedly admitted their involvement in the incident, prosecutors said.
The men are accused of killing Trenton James Cornell-Duranleau, a MI native who had been living in Chicago, last month in Lathems high-rise Chicago condo.
Prosecutors in Chicago revealed details for the first time Sunday in the gruesome homicide there on July 27 that ended with two suspects being arrested and briefly held here in the Bay Area.
Lathem, 46, had communicated for months before with Andrew Warren, 56, about "carrying out their sexual fantasies of killing others and then themselves", Natosha Toller, an assistant Cook County state's Attorney, told the court. On July 27, the pair teamed up to murder 26-year-old Trenton Cornell-Duranleau inside Lathem's River North apartment, stabbing him a total of 70 times, with such force one of the knives broke.More news: WhatsApp Status is now available on the web
"The heinous facts speak for themselves", said Judge Adam Bourgeois. He arrived in the USA three days before the killing, after being reported missing in Great Britain.
According to the prosecutors, Cornell-Duranleau's last words were to his boyfriend. After showering, Lathem and Warren left the apartment an hour after the stabbing began, the prosecutor said.
Police say Lathem and Cornell-Duranleau, who moved to Chicago from the Grand Rapids, Michigan, range about a year prior, had an individual relationship, however they have not portrayed the idea of it or a rationale in the assault.
Cornell-Duranleau later succumbed to the knife wounds, bleeding to death in his boyfriend's condo.
Lathem cried to Warren for help, Toller said, so Warren walked in and put his hands on the victim's mouth, then hit him in the head with a heavy metal lamp.
"I can not reconcile what I have heard on the news with the person that I know", said a woman who had written that she had known Lathem since their undergraduate days at Vassar College. Cornell-Duranleau asked Lathem, according to prosecutors.
The results of a post-mortem examination, announced last Friday, found methamphetamines in Cornell-Duranleau's system. Prosecutors said the men attacked Cornell-Duranleau, 26, as he slept, stabbing him 70 times.
The attack was so intense that it almost decapitated him.More news: Pakistan all set to host World XI in September
The two had planned to kill other people, then each other, prosecutors said.
Lathem and Warren both showed up in court in California a week ago, where they consented to come back to IL to confront charges.
Instead, the men cleaned themselves up and fled the condo, renting a auto together before beginning their apparent cross-country getaway road trip, prosecutors alleged.
Chicago police have said Cornell-Duranleau suffered more than 40 stab wounds, including mutilations, to his upper body.
Warren did not help Cornell-Duranleau.
All of the 32 letters filed with the court by Lathem's attorneys were dated within days of the date the two men surrendered to police in Northern California, and before details of the killing were made public.
Lathem sent a video message to his parents and friends while on the run, admitting to killing his boyfriend, saying "he is not the person people thought he was", according to Toller.
"What they discovered in that apartment can only be described as savage and grisly and shocked what is otherwise a very safe area", Chicago Police Superintendent Eddie Johnson said in a press conference.More news: Trump slams two GOP senators who criticized him on Charlottesville
Prosecutors said that both men have admitted to the slaying, reported the Chicago Tribune. "The court has reviewed his professional and academic achievements - some of the finest in the world".
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