(CNN) Former Illinois police sergeant Drew Peterson was found guilty Tuesday of trying to kill the prosecutor who helped send him to prison for killing his third ex-wife.

Peterson, 62, was convicted of two counts of solicitation of murder for trying to hire a hit man from prison to kill County State's Attorney James Glasgow, Attorney General Lisa Madigan said in a statement.

Glasgow won the 2012 conviction that sent Peterson away for the 2004 murder of Kathleen Savio. Peterson was serving a 38-year sentence for Savio's death when he tried to hire a prosecutor to kill Glasgow between 2013 and 2014, prosecutors said.

Peterson faces a mandatory sentence of 20 to 40 years in prison for solicitation of murder for hire and 15 to 30 years in prison for solicitation of murder, Madigan said. His sentencing is scheduled for July 26.

"The evidence in this case was clear that the defendant plotted from jail to solicit the murder of State's Attorney Jim Glasgow," Madigan said. "I thank the members of the jury for their service, and I commend the prosecutors for their hard work and relentless commitment to bringing this case to a successful conclusion."

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