Trenton Cornell-Duranlow, 26, was found dead with multiple stab wounds on July 27 at the Grand Plaza Apartments on State Street in River North.
Andrew Warren was arrested after he "safely surrendered" himself around 6:30 p.m.to San Francisco police, authorities said.
Warren's city of residence is listed as Oxford on his arrest warrant.
"They knew the seriousness of the charges, the seriousness of the case and how important it was that he be brought into custody, not have to live a life on the run", Conroy said.
Lathem, an associate microbiology professor at Northwestern, was booked into the Alameda County jail. Warren was taken to the San Francisco County Jail. Both Lathem and Warren are being held on no bond status. It was not immediately clear when that would happen. Check with US Marshals Service on specifics of the apprehension.
The two men are expected to first appear before a judge in California before their likely extradition to Chicago.
Both men - taken into custody without incident - will appear before an Oakland court and are now awaiting extradition to IL, where they will be questioned by Chicago homicide detectives.
'Fidgety' Teen Jumps From Plane in SF
The teen was not injured during the incident and his actions did impacted arriving flights at the airport. According to the passengers, the boy seemed too anxious and fidgety throughout the flight.
They apparently stopped in Wisconsin to make a $1,000 donation to the public library in the town of Lake Geneva in the victim's name.
Police said there is no surveillance video of the encounter at the library and were at a loss to explain the donation.
Lake Geneva police said the man making the donation did not give his name.
A spokesperson for the Chicago Police Department told ABC News that authorities believe Lathem "and the victim had a relationship". Law enforcement agencies across the United States have been notified to be on the lookout for the two men, who are considered armed and unsafe. Warren worked as a senior treasury assistant at Oxford's Somerville College in the United Kingdom.
Police have released very few details about the investigation.
Cornell-Duranleau, who grew up in a small town in eastern MI, moved to Chicago past year after getting a job at a salon in the city.
Conroy was not involved in Warren's surrender and did not know how it came about.