By CBS13 Staff

IONE (CBS13) — The notorious serial killer Roger Kibbe was allegedly attacked and killed by his cellmate at Mule Creek State Prison over the weekend.

Early Sunday morning, the California Department of Corrections and Rehabilitation (CDCR) says a correctional officer was doing a population count at the prison when inmate Jason Budrow was spotted standing in his cell with Kibbe unresponsive on the floor.

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Kibbe was taken to the prison’s health care facility, but he was later pronounced dead.

Known as the “I-5 Strangler,” Kibbe was convicted of raping and murdering seven people. The crimes date back to 1977, with Kibbe having been convicted back in 1991 for the murder of Darcie Frackenpohl.

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DNA linked Kibbe to six more murders. In 2008, he pleaded guilty to those murders and was given six more life in prison sentences.

Exactly how Kibbe died is still under investigation, but officials say they are investigating the incident as a homicide. Kibbe was 81-years-old.

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Budrow, 40, was sentenced to life in prison without the possibility of parole for a first-degree murder conviction out of Riverside County. Pending the investigation, Budrow is being housed in a segregation unit.