The use of hearsay testimony to convict former Chicago-area police officer Drew Peterson in the death of his third wife was proper, the Illinois Supreme Court ruled Thursday in upholding the conviction.

The high court, in a unanimous decision , found that hearsay testimony from Peterson's dead third wife and missing fourth wife did not violate his constitutional right to confront his accusers because of evidence that Peterson killed them to prevent their testimony.

The 63-year-old former police sergeant from the Chicago suburb of Bolingbrook is serving a 38-year sentence in the 2004 death of ex-wife Kathleen Savio. He'll follow that with 40 more years after a conviction last year on allegations that he plotted to kill the prosecutor who put him behind bars.

Savio's body was found in a dry bathtub in 2004, weeks before a scheduled hearing to determine monetary and child custody issues related to her divorce from Peterson. Her death was initially ruled accidental, but the case was reopened after the 2007 disappearance of Peterson's fourth wife, Stacy Peterson. Savio's body was exhumed, an autopsy was conducted and her death was ruled a homicide.

Stacy Peterson is presumed dead, though her body has never been found. Drew Peterson remains a suspect in her disappearance, but he has never been charged.

Prosecutors had no physical evidence tying Peterson to Savio's death and no witnesses placing him at the scene, so they relied on hearsay -- statements Savio made to family members and in a written statement to police before she died and that Stacy Peterson made to her pastor and a divorce lawyer before she vanished.

Hearsay is any information reported by a witness that is not based on the witness' direct knowledge. The Illinois court's ruling, written by Justice Mary Jane Theis, found proper use of hearsay -- typically forbidden in criminal proceedings because it can't be challenged -- under a legal doctrine of "forfeiture by wrongdoing."

"We cannot say that the trial court's finding that the state proved that defendant murdered Kathleen to prevent her from testifying was `unreasonable, arbitrary, or not based on the evidence presented,"' Theis wrote.

An attorney for Peterson did not immediately respond to a request for comment on the ruling.

Illinois adopted a hearsay law in 2008 tailored to Drew Peterson's case, dubbed "Drew's Law," which assisted in making some of the evidence admissible.

Peterson was transferred from a state prison in Chester, Illinois, to a federal prison in Terre Haute, Indiana, in February, after Illinois prison officials cited concerns that he posed a security threat.