PHOENIX (Reuters) - A gunman has shot dead a photo radar operator on a busy freeway near Phoenix, police said on Monday.

Police officers were called to the radar enforcement vehicle after reports of gunfire late on Sunday, and they found the employee shot several times, the Arizona Department of Public Safety said in a news release.

The victim, 51, was taken to a local hospital, where he died from his gunshot wounds, the department said. He worked for RedFlex Traffic Systems Inc., which has a contract with DPS to operate photo radar vehicles on the state’s highways.

Police said they were treating the shooting as a homicide and were searching for a man driving a white Chevrolet Suburban, a popular SUV.

Arizona is the first U.S. state to implement a state-wide photo radar system, though similar programs have been used in other countries.