CHICAGO (CBS) — Former Bolingbrook police officer Drew Peterson was sentenced to 40 years in prison Friday for trying to hire someone to kill the prosecutor who helped to convict him in the murder of his third wife.

Peterson, 62, was convicted of trying to hire a fellow inmate’s uncle while in prison to kill Will County State’s Attorney James Glasgow, who helped convict Peterson in 2012 of killing ex-wife Kathleen Savio eight years earlier. Prosecutors say Peterson believed that with Glasgow dead, he could win an appeal of his conviction.

He already was serving 38 years for murdering Savio, and his 40-year sentence in the murder-for-hire plot would begin after he completes that prison term.

Peterson’s fellow inmate, Antonio “Beast” Smith, wore a wire for prosecutors, and jurors heard hours of Smith’s recorded conversations with Peterson at Menard Correctional Center in November 2014. Smith testified last week that Peterson enlisted him to help kill Glasgow.

In one recording, Smith tells Peterson that he gave his uncle the go-ahead to kill Glasgow.

“OK, all right, I’m in,” Peterson, a former Bolingbrook police sergeant, responded. “From the first time we talked about it, there was no turning back.”

Savio’s death was initially deemed accidental. Glasgow reopened the case after the 2007 disappearance of Stacy Peterson, Peterson’s 23-year-old fourth wife.

Peterson was never charged in her disappearance but told the informant he worried that Glasgow would eventually do so.

“This was not merely a threat to one prosecutor,” Glasgow said in a statement Friday. “It was an attack on our entire criminal justice system by a notorious murderer who always felt he could act outside and above the law. Prosecutors across our state must have assurances that they are safe once these criminal enterprises are uncovered.