SACRAMENTO — An inmate who spent nearly three decades on California’s death row has died after being found in his cell, authorities said. Jose Francisco Guerra, 61, was pronounced dead Monday afternoon after he was found unresponsive and alone in his cell at San Quentin State Prison, state prison officials said. The cause of his death will be determined by an autopsy. There were no signs of foul play. Guerra was sent to the nation’s largest death row in 1993 after being convicted of the murder of Kathleen Powell, who was stabbed to death in 1990 at her Los Angeles home. Guerra, a construction worker who was remodeling the house next door, was convicted of first-degree murder during an attempted rape.