Kevin Ray James, 55, of San Bernardino, was arrested for the bank robbery and killing after a joint investigation by the Ventura County Sheriff's Office, Ventura County District Attorney Investigations Bureau and the FBI, officials said.
Further details on the arrest were not immediately available.
On April 28, 1997, two men dressed as construction workers held up Western Financial Bank in Thousand Oaks.
While handcuffing bank teller Monica Leech, one of the robbers shot her in the back of the head. The 39-year-old Camarillo resident died at the scene.
True Crime: The Murder of Monica Leech
True Crime: The Murder of Monica Leech
The suspects drove away in a 1994 Ford Explorer, but crashed nearby. They escaped on foot but the Ventura County Sheriff's Office recovered the vehicle.
Shortly after Leech's killing, local banks and donors raised $160,000 in reward money for whoever turned in the suspects. There was surveillance video. The images weren't great, but they were still usable. Witness descriptions also helped produce composite sketches. And yet - no arrests.
In 2021, a $30,000 reward was offered by the FBI.
Officials plan to hold a news conference Tuesday, where it is expected more information on the arrest will be released.
The Associated Press contributed to this report.