California death row inmate killed after 30-person assault at Kern Valley State Prison

Delano, California – The California Department of Corrections and Rehabilitation is investigating the death of a condemned inmate at Kern Valley State Prison (KVSP) as a homicide, following a violent and chaotic altercation on Friday that escalated into a broader outbreak of inmate aggression.

At approximately 10:30 a.m. on June 6, officials say 36-year-old Mario Renteria, serving a life sentence for first-degree murder and arson, allegedly initiated an attack on fellow inmate Julian Mendez. Prison staff responded immediately, issuing commands for the men to get down. According to CDCR officials, those orders were ignored.

In an attempt to break up the attack, correctional officers deployed chemical agents, temporarily halting the altercation. But within moments, more than 30 other incarcerated individuals rushed at Renteria, striking him repeatedly. Staff then resorted to the use of multiple blast grenades—non-lethal crowd control devices intended to disorient and subdue—to stop the violence.

Mendez, 46, sustained multiple injuries in the assault. Life-saving measures were administered on site before he was transported to the prison’s Triage and Treatment Area, where he was pronounced dead at 11:05 a.m. An improvised weapon was recovered at the scene.

Mendez, originally from Riverside County, had been incarcerated since December 2004. He was sentenced to death in 2002 for the first-degree murder of two teenagers. Renteria, also from Riverside County, entered the prison system in April 2022 under California’s Three Strikes Law. He is being held in restricted housing pending the outcome of the investigation.

In the aftermath of the incident, officials locked down population movement within the facility to facilitate inquiries by the prison’s Investigative Services Unit and the Kern County District Attorney’s Office. The Office of the Inspector General has been notified, and the Kern County Coroner will determine Mendez’s official cause of death.

The scale and intensity of the assault—particularly the mass participation by dozens of inmates—raises concerns about group dynamics and security vulnerabilities within one of California’s most tightly controlled prisons. Opened in 2005, KVSP houses more than 3,100 minimum- and maximum-security inmates and employs roughly 1,500 staff members. The facility offers vocational training and academic programming, though episodes like Friday’s underscore the persistent challenges facing California’s prison system.

As of now, no additional injuries have been reported, and authorities have not said whether further charges will be filed. The investigation remains ongoing.