Susan Russo, who was dubbed the "Black Widow" killer by prosecutors for having her husband murdered in 1994, died of natural causes on Friday, the California Department of Corrections and Rehabilitation reported.
Russo was 67 years old.
Russo was assigned to the Central California Women's Facility in Chowchilla and had been receiving medical treatment at a local medical facility since Aug. 16, according to a CDCR news release.
She was convicted of first-degree murder and conspiracy for the slaying of 43-year-old David Russo. He was a U.S. Navy chief petty officer serving at Lemoore Naval Air Station.
Russo arranged to pay her boyfriend $100 to kill her husband so she could collect benefits as his surviving spouse, including a nearly $1 million insurance policy. She let the boyfriend and an accomplice into her home, where they shot her husband and disposed of his body, authorities say.
Russo was admitted to state prison from Fresno County on Oct. 15, 1996, to serve life without the possibility of parole in state prison.
She was also sentenced for six years for soliciting another person to commit or join in the commission of murder, to be served concurrently.
Former Governor Jerry Brown in 2017 commuted her sentence to 25 years to life, which made her eligible for parole.
In January of 2018, a parole bored ruled in favor of freeing Russo, but Brown blocked her parole. Back then, Brown said she was still a public safety risk who had "more work to do."
Russo had alleged she was been physically abused by her husband. "In my thinking I was protecting myself and my children from an abusive husband and father," Russo wrote in her handwritten 2012 clemency petition.
A parole board investigation into her claims of being battered by her husband came back inconclusive after Brown commuted her sentence.
The Fresno County Sheriff-Coroner Office will determine Russo's official cause of death.
The Associated Press contributed to this report.