Hobbs' partner, who has not been identified, was wounded and taken to the hospital St. Joseph's Hospital and Medical Center, where he remains in stable condition.
"Today is a tragic reminder that our officers risk their lives for us every single day," Phoenix Mayor Greg Stanton told reporters Tuesday.
"This is the worst part of policing, the hard part of policing, the tragic part of policing and the part that always strikes a chord," Phoenix Police Chief Daniel V. Garcia said. Not only for our officers in relation to losing a fellow officer, but for our citizens and, I know, for City Hall.”
The City of Phoenix mourns the loss of veteran Phoenix Police Detective John Hobbs. Keep his family in your prayers. pic.twitter.com/Jpnrg67XGF— Phoenix Fire Dept. (@PHXFire) March 4, 2014
Garcia said that Hobbs and his partner had been pursuing Thornton in a sedan when Thornton crashed at an intersection, got out of his car and "immediately opened fire.". Police said that Hobbs was immediately shot and hit the pavement, but continued to return Thornton's fire.
Hobbs is survived by his wife and three children, ages 10, 8 and 6.
Arizona Gov. Jan Brewer ordered state flags to be flown at half-staff Tuesday.