Further tragedy was avoided by the surrenders of an Oxford University employee and a US professor who spent more than a week on the run as murder suspects, police believe.
Somerville College senior treasury assistant Andrew Warren, 56, and Professor Wyndham Lathem, 42, gave themselves up to police at similar times on Friday evening at separate sites in California, more than 2,000 miles from the crime scene.
They triggered a nationwide manhunt after allegedly stabbing Trenton Cornell-Duranleau, 26, multiple times in Lathem's apartment in Chicago on July 27.
Chicago Police said officers were relieved to hear of the peaceful surrenders after fears grew when Lathem had sent a worrying video to family and friends apologising for his role in the murder.
Force spokesman Anthony Guglielmi said: "Once we got word that Dr Lathem had sent that video to friends and family we began getting concerned that perhaps he would harm himself or this could end up more tragically for both of them, so we are relieved that both of them are safe."
He said the victim and Lathem had been in a "personal relationship" and detectives believe the attack was domestically-motivated, but their connection to Warren is less clear.
Warren was dealing with "personal hardships", had been reported missing from the UK days before the attack and was not on Oxford business, he said.
But Mr Guglielmi added that detectives have unearthed some "online material" that suggests they met on the internet.
They separated at an unknown point as they travelled the US in a "vehicle" before Warren handed himself into a police station in San Francisco and Lathem gave himself up in Oakland.
"Everything was peaceful. Andrew Warren walked into a police station and just said simply, 'I'm Andrew Warren, I'm wanted' and they took him right away," Mr Guglielmi said.
It is not yet known whether their surrenders were co-ordinated and Supervisory Deputy US Marshal Frank Conroy said Lathem's came after lengthy negotiations though his friends and a lawyer.
The Marshal added: "No guns were drawn, he surrendered peacefully and did exactly what he was told to do."
Mr Guglielmi dismissed reports of genital mutilation being involved in Mr Cornell-Duranleau's death, but described a "very violent scene" during which the "body was certainly mutilated".
A broken blade was recovered and officers have CCTV footage tying the men to the 10th floor apartment, he said.
Warren, who says on Facebook he lives in Swindon, and Lathem, a microbiology professor at Northwestern University, now face extradition hearings to determine whether they can be sent to Chicago for questioning.