SAN PABLO (CBS SF) — A third suspect — Tyejuan Shepherd — has been arrested and charged with special circumstances murder in connection with the fatal Sept. 5 shooting of a 20-year-old Richmond man on I-80, San Pablo police said.

Kevin Santisteban was a passenger in a vehicle on I-80 in San Pablo when he was hit by gunfire just after midnight. He was pronounced dead at the scene.

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San Pablo police investigating the shooting identified two Fairfield residents as suspects and arrested them on on Sept. 6.

Jorge Vazquez, 21, was arrested in the 200 block of East Tabor Avenue in Fairfield and Camille McAlister, 23, was arrested later in the day at the San Pablo police station.

Investigators, however, determined a third suspect was involved “and conspired with Vazquez and McAlister to conduct the shooting,” police said.

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They identified the suspect as Shepherd, 18-years-old from Richmond, who was arrested Thursday in El Cerrito.

“Shepherd is believed to have been the person responsible for actually firing the shots during the homicide,” police said.

The Contra Costa District Attorney’s Office reviewed the case and on Tuesday filed murder with special circumstances charges against Shepherd.

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The investigation is ongoing and anyone with information is asked to call (510) 215-3150. Callers can remain anonymous.