An Oxford University employee accused of killing a 26-year-old hair stylist in the United States has been formally charged with murder.

Somerville College senior treasury assistant Andrew Warren arrived in Chicago just before midnight on Friday local time from California.

He and 43-year-old Wyndham Lathem, a former Northwestern University professor, face charges of first-degree murder over the death last month of Trenton James Cornell-Duranleau, a Michigan native who had been working in Chicago.

The authorities say Mr Cornell-Duranleau suffered more than 40 stab wounds to his upper body during the attack in Lathem's high-rise Chicago apartment.

Lathem and Warren, 56, surrendered peacefully to police in northern California on August 4 after an eight-day nationwide manhunt.

Investigators say Lathem had a personal relationship with Mr Cornell-Duranleau.

Warren, who police said had been reported missing from the UK days before the attack and was not on Oxford business, says on Facebook he lives in Swindon.

The findings of a post-mortem were released earlier on Friday, and showed that Mr Cornell-Duranleau had methamphetamine in his system when he was killed.