Authorities say an inmate has been killed at a Northern California state prison and two other prisoners are suspects in his death.

Officials say the 63-year-old man was stabbed with a homemade weapon in an exercise yard Thursday at California State Prison, Sacramento.

Guards saw two inmates fighting with him and used pepper spray and a blast grenade to stop the violence.

The dead inmate was serving life without chance of parole at the maximum-security prison east of Sacramento. His name wasn't immediately released.

One suspect is serving life without chance of parole for a murder in Sacramento County. The other is serving a 22-year sentence for an attempted murder in Orange County.