Officials from the California Department of Corrections and Rehabilitation (CDCR) are conducting an investigation following the death of a death row prisoner at Kern Valley State Prison in Delano on Friday.

Mario Renteria, 36, a convicted murderer, allegedly began assaulting fellow prisoner Julian Mendez, 46, at around 10:30 a.m. on Friday, leading to a response from prison personnel.

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)

According to the CDCR, Mendez had been in custody since December 2, 2004, after being sentenced to death in 2002 for the first-degree murder of two teenagers in Riverside County.

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.