Authorities are investigating the death of an inmate at the California Substance Abuse Treatment Facility and State Prison in Corcoran on Monday, the California Department of Corrections and Rehabilitation said.
Rufus Hodges, 51, was declared dead by medical staff at 8:02 a.m. after he was found unresponsive.
Hodges was serving a life sentence without the possibility of parole for two murder convictions in Riverside County.
The case is being investigated as a possible homicide, prison officials said. His cellmate, Christopher Shirley, was placed in a holding cell as a suspect.
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Shirley, 35, is serving a 46-year, four-month sentence, prison officials said. Shirley was convicted of two counts of assault with a semi-automatic firearm and inflicting great bodily harm on a child under 5 in Shasta County.