RIVERSIDE — A condemned inmate who held a 16-year-old girl captive for weeks in Jurupa Valley, sexually assaulting and torturing her until directing his accomplice to execute the victim, died in a state prison hospice ward, authorities said Tuesday.

Michael Forrest Thornton, 68, of Rialto was at California Medical Facility in Vacaville when he was pronounced dead Monday from an undisclosed terminal illness. Thornton had been moved to the hospice unit from San Quentin State Prison’s Death Row on a date not provided by the California Department of Corrections & Rehabilitation.

In March 2006, Thornton and his co-defendant and girlfriend, now-44-year-old Janeen Marie Snyder, also of Rialto, were both convicted of first-degree murder, attempted sodomy and special circumstance allegations of torturing the victim, killing in the course of a burglary, killing in the course of a sexual assault and killing in the course of a kidnapping.

Snyder was additionally convicted of sentence-enhancing gun and great bodily injury allegations. After a penalty trial that concluded two months later, a six-man, six-woman jury recommended capital punishment for both defendants, which then-Riverside County Superior Court Judge Paul Zellerbach affirmed.

Snyder is incarcerated at the Central California Women’s Facility in Chowchilla.

The pair were notorious for abusing girls and young women, luring them to Thornton’s party pads on the promise of copious free drugs, according to trial testimony. Thornton had once owned a chain of beauty salons before becoming a methamphetamine addict, and Snyder became his partner after his marriage fell apart, testimony revealed.

She was put to work finding vulnerable victims, luring them to Snyder’s lairs, prosecutors said.

The pair abducted Michelle Curran of Las Vegas, who had disappeared in April 2001, using her as an object of sexual abuse and torture for roughly three weeks, during which time she was tied up and restrained, according to testimony. Thornton and Snyder gave the teenager drugs, intimidated her with firearms and sexually exploited her, Zellerbach said during sentencing.

When Thornton became weary of Curran, he directed Snyder to dispose of the teenager, prosecutors said.

The youth’s nude body was discovered in a Jurupa Valley storage shed on April 17, 2001.

The ensuing sheriff’s investigation ultimately led to Thornton and Snyder as the perpetrators, and they were arrested and charged a week later.

Authorities believed the assault was part of a long string of attacks. During sentencing, Zellerbach mentioned other girls that the couple were suspected of stalking and assaulting.

Staff writer Andrea Klick contributed to this report.