California Department of Corrections and Rehabilitation (CDCR) officials are investigating after a death row inmate was killed at Kern Valley State Prison in Delano on Friday.

Convicted murderer Mario Renteria, 36, allegedly started beating fellow inmate, Julian Mendez, 46, at about 10:30 a.m. Friday, prompting prison staff to respond. 

Officers ordered them to get down, but the men failed to comply, according to a CDCR news release obtained by Fox News Digital.

Chemical agents initially stopped the attack, but more than 30 additional inmates rushed Renteria and began striking him.

Julian Mendez was pronounced dead after the jail attack. (CDCR)

Orders to stop were ignored, and staff used multiple blast grenades to quell the violence, according to CDCR.

Mendez suffered multiple wounds, and life-saving measures were immediately taken. He was taken to the prison's triage and treatment area, where a doctor pronounced him dead at 11:05 a.m.

Prisoner Mario Renteria was allegedly the first to attack the death row inmate. (CDCR)

Officials said an improvised weapon was found at the scene, though the type of weapon was unclear.

Renteria remains in restricted housing pending investigation, according to CDCR. 

Officials limited population movement to facilitate the investigation by the prison's Investigative Services Unit and the Kern County District Attorney’s Office. 

The Office of the Inspector General was notified, and the Kern County Coroner will determine Mendez’s official cause of death.

The Kern Valley State Prison attack involved more than 30 inmates in Delano, Calif., on Friday. (Kern Valley State Prison)

Mendez was received from Riverside County on Dec. 2, 2004, according to CDCR. He received a condemned sentence in 2002 for the first-degree murder of two teenagers.

CDCR said Renteria was received from Riverside County on April 27, 2022, and was sentenced to life with the possibility of parole for first-degree murder (a third-strike offense) and arson.

Kern Valley State Prison opened in 2005 and houses over 3,100 minimum- and high-security-custody inmates.