A homicide investigation is underway after Jacob Kober of Livermore was found unresponsive in his cell at the Kern Valley State Prison on Sept. 19. His cellmate, Matthew Perez, was also injured, according to officials.

State corrections officials have launched a homicide investigation after a convicted killer from Alameda County died following an incident at a Central Valley prison Thursday evening.

The Bay Area man was killed last week in a California prison where he'd been serving a life sentence for murdering a close friend, officials said.