Illinois prison officials had convicted wife-killer Drew Peterson transferred to a federal facility last month, deeming him a “threat to safety and security” because he is a former police officer who tried to hire a hitman to kill the prosecutor who put him behind bars.

In February, Peterson was transferred from the Menard Correctional Center to a high-security federal prison in Terre Haute, Indiana.

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At the time, state and federal prison officials declined to explain the reason for the move, but memos obtained from the Illinois Department of Corrections revealed state prison officials sought to move him because they saw him as a “threat to safety and security of the department.”

IDOC acting manager Doug Stephens wrote a letter to IDOC acting director John Bladwin, informing him of the plan to transfer Peterson to federal custody.

“Illinois is seeking placement via the Interstate Corrections Compact Agreement due to his former position as well as his conviction of Solicitation/Murder/For Hire of the Will County State’s Attorney. With his placement outside of Illinois Department of Corrections, it is imperative this offender be continually monitored through his mail as well as telephone conversations due to his former actions,” Stephens wrote.

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IDOC memos obtained through a Freedom of Information Act request also reveal the department’s efforts to keep Peterson’s transfer under wraps as long as possible.

“The information regarding this move should be treated as highly confidential and limited to only staff needed to complete this transfer,” IDOC assignment coordinator Kathy Greer wrote in a memo about the transfer.

Peterson, 63, was sentenced to 38 years in prison for the murder of his third wife, Kathleen Savio. While in prison for that crime, the former Bolingbrook police sergeant was charged with trying to hire a hitman to kill Will County State’s Attorney James Glasgow, who personally prosecuted Peterson’s case. Peterson was sentenced to an additional 40 years in prison for the murder-for-hire plot.

The federal prison in Terre Haute is one of only two in the nation used for inmates whose crimes are considered so serious, that all their communication is under constant monitoring. It is often used for prisoners who violate communication privileges to threaten witnesses, prosecutors, or judges.

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Peterson also has been named as a suspect in the disappearance of his fourth wife, Stacy Peterson, but never has been charged in that case, and she has yet to be found. The search for Stacy prompted authorities to reopen the investigation of Savio’s death, which originally was ruled an accidental drowning. A new autopsy in 2008 ruled Savio’s death a homicide, and Drew was convicted in her death four years later.