Phoenix police spokesman Vincent Lewis said Pitt was shot about 5:30 p.m. and was pronounced dead at the scene, the Arizona Republic reported.
Witnesses told police they heard a loud argument, followed by shots, the Republic reported.
"We are not ruling anything out, but at this point, a loud argument probably suggests they knew each other either professionally or personally," Lewis told NBC News.
According to Pitt's website, he conducted forensic psychiatric evaluations in the Phoenix Police Department's Baseline Killer task force. Pitt's work helped police arrest Mark Goudeau in 2006 after nine people were murdered, the Republic reported.
Pitt previously practiced in Colorado, and was asked to assist in the homicide of Benet, who was murdered in 1996.
"He gave us insights in terms of 'profiling' people that we were looking at that I thought were beyond all of our expertise, important, helpful stuff," Hunter told the Phoenix New Times in 1999. "He's tough and tenacious, and he isn't just a book kind of guy. He was particularly valuable in giving us suggestions about the order and timing and nature of the questions we'd be asking the Ramseys. He always has had extremely strong feelings about the case, which, to put it mildly, he wasn't afraid to share."
Pitt also consulted on the 1999 Columbine High School shooting, the Republic reported.
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