Cellmate detained after inmate convicted of sexual assault found dead at California prison

Authorities in California have launched a homicide investigation following the death of an inmate at California State Prison, Sacramento, as disclosed on Wednesday.

The California Department of Corrections and Rehabilitation (CDCR) reported that 49-year-old John Cisneros was discovered unresponsive in his cell around 9:15 p.m. on February 23.

Efforts to resuscitate Cisneros were immediately initiated by medical staff, but he was declared deceased shortly before 10 p.m.

Coils of razor wire line a tall security fence outside a prison housing unit in Represa, California.

An image captured on April 13, 2023, shows razor wire crowning a fence near the Short-Term Restricted Housing Unit at California State Prison, Sacramento, in Represa, Calif. (Photo by Luis Sinco/Los Angeles Times via Getty Images)

Cisneros’ cellmate, Irvin Sanchez, aged 34, was taken into custody and relocated from the cell.

Sanchez is currently being held in restricted housing as the prison’s Investigative Services Unit, in collaboration with the Sacramento County District Attorney’s Office, conducts a thorough investigation.

The Office of the Inspector General has also been notified.

A split of John Cisneros (right) and Irvin Sanchez (left).

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.

A grid of small, caged outdoor enclosures sits beside a prison building in Represa, California.

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)

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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