Though Drew Peterson was tried and convicted of murdering Kathleen Savio, the former police sergeant's missing fourth wife had a constant presence during the trial.
"They tried keeping her out of that courtroom, and eventually two profound statements were made by her, and that's what did it," said Pamela Bosco, a spokeswoman for the family of Stacy Peterson, who vanished in October 2007. "They sealed his fate."
Prosecutors suspect Drew Peterson killed sandy-haired Stacy Peterson because she could finger him for Savio's death, but her body has never been found and no charges have ever been filed.
Stacy Peterson told friends and family that she woke up Feb. 29, 2004, in the middle of the night to find her husband gone. Kathleen Savio's body was found March 1, 2004, in the bathtub of her home, blocks from the Petersons' Bolingbrook, Ill., home. Stacy Peterson later told friends and family her husband asked her to lie about seeing him return home with women's clothing that did not belong to her.
Judge Edward Burmila barred any mention of Stacy Peterson's disappearance during the trial, but jurors heard from her through the testimonies of Rev. Neil Schori and attorney Harry Smith.
Schori said Stacy Peterson told him Drew Peterson disappeared from their home around the time of Savio's death. Smith testified that Stacy Peterson called him days before her disappearance and "wanted to know if, in my opinion, the fact that he killed Kathy could be used against him."
Illinois State Police declared Drew Peterson a suspect in Stacy Peterson's disappearance on Nov. 9, 2007, the same day they formally launched an investigation into Savio's 2004 drowning death and a judge signed an order to exhume Savio's body.
Drew Peterson contends his fourth wife ran off with another man and is still alive.
"Stacy's case is next, no matter what," Bosco told reporters Thursday after a seven-man, five-woman jury found Peterson guilty in Savio's death. "We still have to pay the price for Stacy. I still believe that's around the corner."
Stacy Peterson's sister, Cassandra Cales, said the family is in constant contact with police and hopes someone will come forward with new information. "This is the first step," Cales said.
James Glasgow, Will County state’s attorney, told reporters outside the Joliet courthouse that prosecutors plan to review the evidence in Stacy's disappearance and "aggressively" seek to charge Peterson if possible.
"Obviously the longer any person is gone, the easier it is to prove that they haven't just simply run away and that they are deceased," Glasgow said. "October 28 of 2007 is way in our rear-view mirror now, so we're going to look at that case and assess it as it stands today. If we feel confident that we can go forward, we will be doing so."
Savio learned in 2001 that Drew Peterson was having an affair with Stacy Cales, a 17-year-old hotel clerk at the time.
Drew Peterson and Savio were granted a divorce on Oct. 13, 2003, and he married in Stacy on Oct. 18 when he was 49 and she was 19. They had two children, Anthony and Lacy.
Stacy Peterson was reported missing Oct. 29, 2007, a day after she failed to show up at a relative's home.
Stacy's family said they never will give up hope.
"I love you and I miss you," Cales said when asked what she wanted to tell her missing sister, "and I'm never going to give up hope in finding you."
"We miss you," Bosco said, choking back tears. "This man has to pay for Stacy."
NBC News' Jim Gold contributed to this report.
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