SAN QUENTIN (CBS SF) — A San Quentin State Prison death row inmate convicted of killing an armored car guard in Southern California was found dead in his single-inmate cell Wednesday afternoon.

Henry Abbott, 48, was found unresponsive at 3:23 p.m. and was pronounced dead at 4:09 p.m., the California Department of Corrections and Rehabilitation said. The cause of death is pending an autopsy.

A San Bernardino County jury sentenced Abbott to death on Feb. 17, 2006. Abbott was convicted of the first-degree murder and robbery of Brinks armored car guard Samuel Saenz on Oct. 30, 2000.

Abbott shot Saenz in the back of the head as Saenz left the Bank of America in Ontario with a large white bag that contained $202,292, according to the CDCR.

Abbott grabbed the bag and shot Saenz a total of three times before fleeing with accomplices. The bag was never found.

He surrendered to the Los Angeles County Sheriff’s Department on Nov. 15, 2000 and has been on death row since Feb. 22, 2006, the CDCR said.