A high-profile forensic psychiatrist who advised police and prosecutors in high-profile cases like the JonBenet Ramsey murder and the Columbine school massacre was shot dead outside his Arizona office on Thursday evening.

Steven Pitt, 59, was leaving his office for the day when witnesses heard a loud argument and then gunshots, Phoenix Police Sgt. Vince Lewis said. The witnesses provided a description of the gunman that allowed police to create a sketch.

Forensic psychiatrist Steven Pitt was killed outside his office. 12 News

"We are not ruling anything out, but at this point, a loud argument probably suggests they knew each other either professionally or personally," said Lewis, adding that officers were still canvassing for possible surveillance video.

Pitt had worked as a consultant for law enforcement across the country, helping investigators understand the dynamics between suspects and victims and map out interrogation strategies. He was frequently quoted as an expert by national media outlets, including NBC News.

Phoenix police said they have not yet determined a motive for the shooting. But they are keeping the nature of Pitt's work in mind.

"It's an angle we'll be looking into," Lewis said.

Sketch of suspect in the fatal shooting of Steven Pitt. Phoenix Police Department

A crime buff from an early age, Pitt used to practice in Colorado, where he was tapped by Boulder County District Attorney Alex Hunter to assist in the 1996 homicide of child beauty queen JonBenet.

"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 would later tell the Phoenix New Times.

"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."