"Custody staff immediately began life-saving measures and transported Castañeda to a medical building," California Department of Corrections and Rehabilitation officials said in a news release. "The Folsom Fire Department arrived shortly after and Castañeda was pronounced dead at 10:51p.m."
Investigators developed Arthur Gene Lane as a suspect and subsequently moved Lane, 47, to the prison's administrative segregation unit, the news release said. The Sacramento County District Attorney's Office is assisting prison officials in the investigation.
The prison, situated adjacent to the historic Folsom State Prison, is also known as New Folsom. According to CDCR officials, it is a high-security prison that houses more than 2,100 general population inmates and employs about 1,700 people.
The prison houses long-term inmates, inmates who need specialized mental health care and inmates with high-risk medical concerns.
Castañeda had been in prison since March 2014. He was initially imprisoned on a three-year sentence for a robbery in Los Angeles County, but had another four years added to the sentence on a battery charge out of Monterey County.
He had also previously served prison time in 2012 in connection with a Riverside County case of injury to an elder causing death or great bodily injury, the news release said.
Lane has been in prison since January 2003 on the first-degree murder charge out of Sacramento County. While in prison, he was convicted of assault with a deadly weapon on another inmate, the release said.
The Napa Valley Register reported in June 2001 that Lane, then 30, had been arrested in the death of Nancy Mae Paul, who was hanged in the garage of Lane's home the month before. Paul, 27, was initially believed to have killed herself after Lane told detectives they had broken up just before she went into the garage.
Investigators soon got a tip from a friend of Paul’s, who found a videotape Lane made of the homicide. According to media reports at the time, the video showed Paul standing on a chair as Lane placed a noose around her neck and kicked the chair away.
Her last words were, "I'm gonna die," according to a 2002 Sacramento Bee story.