Illinois wanted Drew Peterson out of its prison system because he is a former cop who tried to have Will County State’s Attorney James Glasgow killed.

That was the reason given by the Illinois Department of Corrections in an Oct. 5, 2016, memo obtained by the Chicago Sun-Times seeking a transfer for the notorious wife killer. Written by IDOC acting manager Doug Stephens, it noted that it is “imperative” that Peterson “be continually monitored through his mail as well as telephone conversations.”

“Peterson is a threat to safety and security of the department,” Stephens wrote.

Peterson, a former Bolingbrook police sergeant, landed in a federal prison in Terre Haute more than two weeks ago. The sudden transfer has only now been explained by the release of the IDOC records. Even Peterson’s attorney claimed to be in the dark until now. But the IDOC records indicate the 63-year-old’s transfer had been in the works for at least four months, and he was designated to the Terre Haute prison about a month ago.

One email sent Feb. 16 by IDOC assignment coordinator Kathy Greer noted that information regarding Peterson’s move out of Menard Correctional Center “should be treated as highly confidential and limited to only staff needed to complete this transfer.” In another email, Greer asked the Menard warden to “please involve minimal staff in this as it is confidential.”

Finally, Greer noted in an email that “since this is an involuntary movement, the department will have to pay” for the delivery of Peterson’s personal property.

Peterson has long been suspected — but never charged — in the disappearance nearly a decade ago of his fourth wife, Stacy Peterson. After she vanished, prosecutors put Peterson on trial in 2012 for the 2004 murder of his third wife, Kathleen Savio, whose death had previously been ruled an accident. A Will County jury convicted him, and a judge sentenced Peterson to 38 years in prison. Peterson predicted he would die there.

Then, while serving his sentence at the downstate Menard prison, Peterson became friends with a Satan’s Disciple known as “Beast.” That man’s real name was Antonio Smith, and he would eventually wear a wire while Peterson fantasized about the murder of Glasgow, the elected Will County state’s attorney who led the 2012 prosecution of Peterson.

Prosecutors in downstate Randolph County charged Peterson in the murder-for-hire plot, and jurors convicted Peterson after a roughly week-long trial last year. A judge then sentenced Peterson to another 40 years in prison.

He is now scheduled for release on May 7, 2081.