SAN QUENTIN, Calif. (AP) — An inmate on California’s death row died of unknown causes at San Quentin State Prison, corrections officials said Thursday.

Charles Edward Crawford II, 46, was found unresponsive in his cell on Wednesday morning, the California Department of Corrections and Rehabilitation said in a statement. He was taken to a hospital where he pronounced dead 12 hours later.

READ MORE: Woman Drowns At Shrinking Folsom Lake, Leaving Young Nephew Alone on Shore

The Marin County Coroner’s Office will determine the cause of death.

READ MORE: Stockton Surveillance Video Appears To Show Woman Being Abducted

Crawford was sentenced to death in Alameda County on June 7, 2002, for killing a 16-year-old San Jose girl and a Fremont man.

MORE NEWS: State Water Officials Preparing To Make Emergency Cutbacks To Growers And Ranchers

San Quentin, north of San Francisco, is California’s oldest prison. It houses the state’s death row as well as general population inmates.