MARIN COUNTY (KRON) — A death row inmate at San Quentin State Prison in Marin County died of unknown causes Wednesday evening, according to the California Department of Corrections and Rehabilitation.

67-year-old Raymond Edward Steele was pronounced dead at 7:37 p.m. after being found unresponsive in his cell.

The cause of Steele’s death is autopsy-pending according to CDCR officials.

Steele was sentenced to death in 1990 for fatally stabbing a mentally handicapped woman in Shasta County in 1988. He had a prior conviction for rape in 1971 as well as for the second-degree murder of his 15-year-old babysitter, CDCR officials said.

Steele had been on death row almost 25 years.