CHICAGO (CBS) — Convicted killer Drew Peterson, serving a total of 78 years in prison, was transferred out of state custody on Tuesday to a federal prison in Terre Haute, Ind.

“Drew Peterson (Reg. No. 07018-748) is in the custody of the Federal Bureau of Prisons at the United States Penitentiary in Terre Haute,” said Jill Tyson, spokeswoman for the Federal Bureau of Prisons.

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The reason for the move from state to federal custody has not been released. Neither the Bureau of Prisons or the Illinois Department of Corrections would explain the transfer.

“Drew Peterson has been transferred out of IDOC custody. For safety and security purposes, the IDOC does not discuss details concerning the placement of offenders who are transferred under the terms of the Interstate Compact Agreement,” Illinois Department of Corrections spokeswoman Nicole Wilson said in an email.

CBS 2 Legal Analyst Irv Miller said there are several possible reasons.

“His own security, they can’t protect him. Two, he’s a witness on a federal case that we don’t know about. Or three, he’s been indicted himself,” Miller said.

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The Will County Sheriff’s office confirmed Peterson was first moved to the Stateville Northern Reception and Classification Center, which is used for processing prisoner transfers in Illinois.

In 2013, Peterson was sentenced to 38 years in prison for the murder of his third wife, Kathleen Savio. While in prison for that crime, he was convicted of trying to hire a fellow inmate to kill Will County State’s Attorney James Glasgow, and was sentenced to an additional 40 years in prison.

Peterson, a former Bolingbrook police sergeant, has been named a suspect in the disappearance of his fourth wife, Stacy Peterson, in 2007, but has not been charged in that case.

As authorities were investigating Stacy’s case, they also reopened the investigation into Savio’s death, which originally was ruled an accidental drowning. A new autopsy later ruled Savio’s death a homicide, and Peterson was convicted of her murder.

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Peterson’s son, Stephen, recently revealed he believes his father “probably” killed both Kathleen Savio and Stacy Peterson.