SACRAMENTO, Calif. — A San Francisco Bay Area serial killer has died of unknown causes on California’s death row, officials said Friday.

Condemned inmate Anthony McKnight, 65, was found unresponsive in his San Quentin State Prison cell Thursday night and pronounced dead shortly thereafter.

The cause is awaiting an autopsy, but corrections spokeswoman Terry Thornton said there is no reason to suspect foul play.

The ex-Navy sailor was sentenced to die in 2008 after Alameda County investigators linked his DNA to five young women slain in 1985: Betty Stuart, 22; Diane Stone; 17; Talita Dixon, 13; Monique Davis, 18; and Beverly Bryant, 24.

The special circumstances that led to the death penalty included that he committed the multiple murders in the course of rape and sodomy.

Alameda County Superior Court Judge Jeffrey Horner said during sentencing that he “butchered” his victims, who were beaten to death.

The trial focused on DNA evidence that had been collected at the time but wasn't analyzed until the late 1990s, when new techniques became available.

The discovery came after he had already been in prison since 1987, serving a 63-year sentence for attempted murder, rape with force, assault with a deadly weapon, oral copulation and kidnapping to commit a sex offense.

He was convicted in that case of raping and trying to murder three other women, all of whom testified in his trial.

Earlier this year, Gov. Gavin Newsom imposed a moratorium on the death penalty so long as he is governor, leaving 731 inmates on the nation’s largest death row.