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: Who Is Mark Lavea, Suspect Killed In San Andreas Hostage Situation?

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

READ MORE: Trap, Tag, Haze: New Efforts To Get Bears To Behave In Tahoe Area

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: Yuba City Neighborhood 'Traumatized' After High Speed Drivers Repeatedly Crash Into Homes

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