Lt. Ron Raman said police are actively searching for 22-year-old Brian Keith Fox in connection with the shooting, which happened around 9 a.m. at the Union 76 gas station at 2150 Railroad Ave.
Fox is considered armed and dangerous.
Raman said officers arriving at the scene located the victim, a 20-year-old Pittsburg resident who had been shot in the head.
The man was taken to a hospital, where he succumbed to his injuries this afternoon. His name has not been released.
Using witness descriptions, officers were able to track down the suspect vehicle, which was found parked in front of a home in the 100 block of Marin Avenue in Bay Point later this morning, Raman said.
Contra Costa County sheriff's deputies and Pittsburg police spoke to residents inside the home where the car was parked but did not locate Fox.
A motive for the shooting has not been determined, but police believe the victim was targeted, he said.
Anyone with information about Fox's whereabouts is asked to call Pittsburg police at (925) 646-2441.
