SACRAMENTO (AP) — Four inmates were killed at three state prisons in Northern and Southern California, corrections department officials said Monday.

“They’re all unrelated,” said department spokeswoman Terry Thornton.

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Robert Beltran, 50, was fatally stabbed by three other inmates as he left his cell at Kern Valley State Prison in Delano on Friday, officials said.

That’s in a different part of the same prison where a day earlier officials previously said two inmates fatally stabbed convicted murderer Robert Hargrave, 48.

Beltran was serving a life term for attempted second-degree murder and kidnapping. Officials did not immediately say if they had any reason to think the two slayings are related.

The three being held on suspicion of killing Beltran are Charles Garibay, Rafael Navarro and Guillermo Navarro. The victim and suspected attackers are all from Los Angeles County.

Guillermo Navarro, 38, is serving a life term for murder. He is not related to Rafael Navarro.

Rafael Navarro, 32, is serving a 25-year sentence for armed robbery with gang enhancements. He has additional sentences for drug possession and attacking another inmate while in prison.

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Garibay, 34, is serving a 46-year sentence for assault with a semi-automatic firearm on a peace officer, attempted carjacking and attempted murder, and another four years for possessing a weapon in prison.

Also on Thursday, 260 miles to the north, officials at the California Medical Facility in Vacaville said they found 75-year-old Tuc X. Tran unresponsive in his cell with multiple injuries to his head and face. His next of kin were notified on Monday. He had been serving a life sentence for a Riverside County murder.

They are holding his cellmate, James A. Norton, 39, as a suspect. He is serving a two-year sentence from Mendocino County for causing a fire on forest land.

The fourth slaying was Friday at High Desert State Prison in Susanville.

Officials say two inmates fatally stabbed Michael M. Ramadanovic, 65, and didn’t stop until correctional officers used chemical agents and fired a warning shot. He was serving a life sentence for a Merced County murder, with another six-year sentence for assault with a deadly weapon in prison.

The two suspects are Rodney Rice and Robert Smith, both 28. Officials did not immediately provide their criminal histories.

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