(KTXL) — The California Department of Corrections and Rehabilitation said it is investigating a death at High Desert State Prison as a homicide.

Brandon Martinez, of Yuba County, and Pedro Ayon, of Tulare County, allegedly attacked an inmate on Saturday evening. 

Staff at the prison noticed the incident and intervened, taking the victim to emergency services. However, he was pronounced dead not long after. 

The CDCR identified the victim as 43-year-old Jeffrey Concepcion. 

Ayon, 30, and Martinez, 25, were placed into restricted housing after the attack. 

According to the CDCR, Concepcion was serving a life sentence for first-degree murder, second-degree robbery and attempted second-degree murder. He had been in the custody of the CDCR since 1999. 

Martinez has been in custody since 2016 for one count of assault with force likely to produce great bodily injury, one count of second-degree robbery and assault with a deadly weapon. His sentence was 18 years and eight months. 

Ayon has been serving a 27-year and two-month sentence since 2012 for two counts of second-degree murder, one count of assault with force likely to produce GBI, one count of second-degree robbery and one count of attempted carjacking.