CHICAGO, Illinois (CNN) -- A pathologist has determined that the death of the third wife of former police Sgt. Drew Peterson was a homicide, James Glasgow, the state's attorney in Will County, said Thursday.
Investigators have said Drew Peterson is a suspect in the disappearance of his fourth wife, Stacy Peterson.
"We have been investigating this as a murder since reopening the case in November of last year," Glasgow said in a written statement.
"We now have a scientific basis to formally and publicly classify it as such."
Suspicions surrounding the disappearance of Peterson's fourth wife, Stacy Peterson, prompted authorities to exhume the body of Kathleen Savio late last year.
Savio was found drowned in a bathtub in 2004, but her death was originally ruled an accident.
Certified forensic pathologist Larry Blum conducted the autopsy on Savio after Glasgow said additional information turned up during the investigation into Stacy Peterson's vanishing that raised questions about the death of Savio. Watch Savio's sister discuss her suspicions of Peterson »
The new autopsy results have left Stacy Peterson's loved ones with "an eerie feeling of dread," said Pam Bosco, a spokeswoman for her family.
"We realize that Kathleen and Stacy had one common denominator, and that's Drew Peterson," she told reporters Thursday evening in Bollingbrook, Illinois.
"I can't help but feel extreme sadness for Kathleen, because she did cry out so many times, but it seems like it fell on deaf ears. Now that this information comes out, we can only hope that we find the person that did this horrible thing to her," Bosco said.
Drew Peterson, 53, said he last spoke to his 23-year-old wife Stacy the night of October 28, 2007. She has been missing ever since. Timeline: Learn more about the events of the case »
Illinois State Police have named him a suspect in the case, but he has consistently denied any involvement in her disappearance.
Peterson told the media he believed she ran off with another man.
Drew and Stacy Peterson have been married four years and have two children. Drew also has older children from a previous marriage. E-mail to a friend
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