California prison officials are investigating the death of an incarcerated man at California State Prison, Sacramento, as a homicide, authorities announced Wednesday.

Staff found 49-year-old John Cisneros unresponsive in his cell at about 9:15 p.m. local time on Feb. 23, according to the California Department of Corrections and Rehabilitation (CDCR).

Medical personnel began life-saving measures, but he was pronounced dead just before 10 p.m.

Razor wire tops a fence near the Short-Term Restricted Housing Unit at California State Prison, Sacramento, in Represa, Calif., on April 13, 2023. (Luis Sinco/Los Angeles Times via Getty Images)

Cisneros’ cellmate, 34-year-old Irvin Sanchez, was detained and removed from the cell.

He has since been placed in restricted housing pending the outcome of an investigation by the prison’s Investigative Services Unit and the Sacramento County District Attorney’s Office.

The Office of the Inspector General has also been notified.

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John Cisneros (right) was found unresponsive in his cell at California State Prison, Sacramento, on Feb. 23, 2026. His cellmate, Irvin Sanchez (left), was detained following Cisneros’ death. (California Department of Corrections and Rehabilitation)

The Sacramento County Coroner’s Office told Fox News Digital the cause and manner of death remain pending and that final reports could take at least six months from the date of death to complete.

Cisneros was originally sentenced in 2015 to five years for second-degree robbery. 

While incarcerated, he was later sentenced in 2017 to 28 years for “penetration, oral copulation and attempted rape with force/violence/fear of immediate bodily injury,” according to CDCR.

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Rows of individual exercise yards stand outside the Security Housing Units at California State Prison Sacramento on March 5, 2014, in Represa, Calif. (Michael Macor/San Francisco Chronicle via Getty Images)

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Sanchez is serving an 18-year sentence for attempted second-degree murder with gang and firearm enhancements.

California State Prison, Sacramento, currently houses more than 2,200 medium-, maximum- and high-security incarcerated men.

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