SACRAMENTO (CBS13) — Convicted serial killer Roger Kibbe – who was killed behind bars over the weekend – was strangled to death, according to autopsy results released on Wednesday.

Known as the “I-5 Strangler,” Kibbe was serving consecutive life sentences for killing seven women over two decades.

Kibbe was found unresponsive in his Mule Creek State Prison cell on Sunday and was later pronounced dead. His cellmate, Jason Budrow, is accused of killing him.

His victims’ families told CBS13 this week that Kibbe’s death was deserved.

“I don’t have any sympathy for him at all,” said Carl Burleigh, who’s sister Lou Ellen Burleigh was Kibbe’s first known murder victim in 1977.

The former lead homicide detective with the San Joaquin County Sheriff’s Office also said he believed there were more victims tied to Kibbe’s murder spree.

“Absolutely. He’s responsible for many more,” Vito Bertocchini told CBS13.

According to the Amador County Sheriff’s Office, Kibbe’s autopsy found his cause of death to be manual strangulation. The incident is being investigated as a homicide.

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Budrow is being held in an administrative segregation unit pending the investigation.