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An infamous inmate, who murdered a serial killer in his prison cell three years ago, pleaded not guilty to a prison ambush of Kristin Smart's killer.

Jason Budrow, 43, allegedly made a shank and slashed Paul Flores in the neck during an Aug. 23 jailhouse attack a week after Flores was transferred to the Pleasant Valley State Prison in Coalinga, California.

"Yard staff saw Flores fall to the ground between the recreational yard and the medical clinic," the California Department of Corrections and Rehabilitation (CDCR) told Fox News Digital after the alleged assault.

On Monday, Budrow pleaded not guilty to four felony charges, including using a prison-made deadly weapon and assault by an inmate serving a life sentence.

KRISTIN SMART'S KILLER NEARLY DIED DURING ALLEGED PRISON ATTACK WHO MURDERED ‘I-5 STRANGLER’

Jason Budrow, 43

Jason Budrow, who murdered the "I-5" strangler in jail, allegedly attacked Kristin Smart's killer Paul Flores in prison. (California Department of Corrections and Rehabilitation )

Flores was rushed to an outside hospital in serious condition, where he stayed for two days before returning to prison, according to the CDCR.

The CDCR declined to answer Fox News Digital's questions in November about the incident, including how Budrow got access to Flores or where Budrow and Flores are currently being housed.

KRISTIN SMART KILLER PAUL FLORES SENTENCED TO 25 YEARS TO LIFE FOR CALIFORNIA MURDER

And authorities still haven't mentioned a possible motive for the alleged attempt on Flores' life. 

Flores is serving a 25-years-to-life sentence for murdering 19-year-old Smart in 1996, when they were both students at California Polytechnic State University, San Luis Obispo.

He was convicted in the decades-old cold case, even though Smart's body was never found. She was declared legally dead in 2002.

Left: Still-missing college student Kristin Smart; Right: Paul Flores

Kristin Smart's murderer, Paul Flores, was attacked in prison and hospitalized in serious condition, according to his lawyer. (FBI/San Luis Obispo County Sheriff's Office via AP)

He crossed paths with Budrow, a self-described Satanist who sports a "666" tattoo above his right eye, a week after being transferred to the California prison. 

Budrow was already serving two life sentences without parole for fatally strangling his girlfriend in 2010 and strangling his Mule Creek State Prison cellmate – Roger Reece Kibbe, 81 – in 2021.

Kibbe was known as the "I-5 Strangler" in the 1970s and 1980s because he hunted women along the Interstate 5 corridor between Sacramento and Stockton.

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He raped and strangled at least seven women and was known for cutting his victims' clothing into irregular patterns.

Budrow said in a letter to the San Jose Mercury News that he purposely arranged to get a cell with Kibbe after seeing the TV coverage and killed him because he was on "a mission for avenging" Kibbe's victims.

If convicted on the new charges, Budrow could receive an additional sentence of 27 years to life in prison.