Officials say yard officials at the California Substance Abuse Treatment Facility in Corcoran found 21-year-old Shawn G. Jackson Jr. unresponsive around 1:30 pm on July 18.
Medical staff was called and he was taken to a nearby hospital in Hanford, where he later died.
Investigators later determined that 31-year-old Jarvis Richerson had attacked Jackson.
Authorities say the Office of the Inspector General and Office of Internal Affairs were notified.
The Kings County coroner will determine Jackson's official cause of death.