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)

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.