An Illinois jury finds the former cop guilty of murdering his third wife. NBC's Chris Clackum reports.

JOLIET, Ill. — A jury on Thursday found Drew Peterson guilty of first-degree murder in the 2004 drowning death of his third wife, Kathleen Savio.

There were loud gasps in the courtroom as the verdict was delivered.

Peterson, a former Chicago-area police sergeant, sat stoically and did not react, and then was cuffed and led away from the courtroom.

When Savio was found dead in a bathtub, the death was initially ruled accidental. The 2007 disappearance of Peterson's fourth wife, Stacy Peterson, raised suspicions.

Read more about the case at NBCChicago.com

Little physical evidence linked Peterson to Savio's death, and the prosecution's case relied heavily on testimony from people who said Peterson threatened Savio, tried to hire a hit man and warned he could make her death look like an accident.

A seven-man, five-woman Will County jury spent about 14 hours deliberating over whether to convict Peterson on a case based solely on hearsay and circumstantial evidence. In the end, the words of Savio’s friends, family and close relations were enough to convince them of his guilt.

Outside the courthouse, people cheered, NBC station WMAQ of Chicago reported.

Former police sergeant Drew Peterson in booking photograph released by the Will County Sheriff's Office on May 8, 2009.

"This is better than the White Sox winning the World Series," Savio's brother, Nick Savio, said through tears outside the courthouse.

"We got the bastard," Savio’s brother-in-law, Mitch Doman, said as he left the courtroom, the Chicago Sun-Times reported.

Peterson "will never be able to hurt another woman again," Pam Bosco, spokeswoman for the family of Stacy Peterson, said outside the courtroom, the Sun-Times reported.

Bosco said the verdict is partial justice for Stacy Peterson because statements she made before vanishing were heard in the courtroom through testimony of other witnesses at the trial.

AFP - Getty Images file Drew Peterson's fourth wife, Stacy Ann Peterson, who has been missing since 2007. It was her mysterious disappearance that prompted state prosecutors to pursue charges against Drew Peterson in the death of his third wife, Kathleen Savio. A jury convicted him of first-degree murder on Thursday.

Hearsay, or a statement not based on the direct knowledge of a witness, isn't usually admissible in court, but Illinois passed a law in 2008, dubbed "Drew's Law," that allowed it in rare circumstances.

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So what happened to Stacy Peterson?

Peterson and Savio were divorced a year before her death. Prosecutors argued that his motive for killing her was fear that a pending settlement in the split would wipe him out financially.

Throughout five weeks of testimony, jurors heard of Savio's purported conversations with family and friends about threats Peterson allegedly made against her. In one, Savio said Peterson once held her captive at knife-point in her own home. In another, she said her husband told her he could kill her and make it look like an accident. Another witness said Savio was so fearful of Peterson that she slept with a knife beneath her bed.

Jurors also heard the purported words of Stacy Peterson through the testimony of divorce attorney, Harry Smith, who spoke to her by phone just days before she vanished.

Her body has not been found and no charges have been filed in connection with her disappearance.

M. Spencer Green / AP Marcia Savio, step-mother of Kathleen Savio cries outside the Will County Courthouse after word that Drew Peterson was found guilty of murdering his third wife Kathleen Savio. She is accompanied by Kathleen Savio's half-brother Nicholas Savio.

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Judge Edward Burmila barred any mention of Stacy's disappearance during the trial and it was unclear what the jury, which was ordered to avoid media coverage of the case for nearly two years, knew about her or the fact that she's still not surfaced.

It's not immediately clear how much credence jurors gave to the forensic testimony given by a bevy of pathologists. State witnesses were adamant Savio's death was a homicide. Defense witnesses said precisely the opposite.

Peterson now faces a maximum 60 years in prison when he's sentenced Nov. 26. It's not immediately clear if Burmila will take into account the nearly three years Peterson has already spent in jail awaiting trial.

Will County State's Attorney James Glasgow speaks outside an Illinois courthouse, where Drew Peterson was found guilty of killing his third wife, Kathleen Savio.

See previous NBC News stories on the case

Whatever the sentence, it could be cut drastically shorter if appeals promised by his defense team are upheld by a higher court. The trial was threatened three times by a mistrial after prosecutorial missteps, errors Peterson's legal team will no doubt attempt to exploit.

Speaking to reporters after the trial, Defense Attorney Joel Brodsky promised an appeal.

"Believe me, there's several world-class appellate lawyers that are just waiting to get their teeth into this case," he said.

State's Attorney James Glasgow also spoke to reporters, saying that prosecutors would "aggresively review" the disappearance of Stacy Peterson and potentially pursue additional charges against Peterson.

A legal analyst on NBC Chicago said that the prosecutors would, at a minimum, likely use the fourth wife's disappearance in its argument for more jail time at Drew Peterson's sentencing hearing scheduled for Nov. 26.

During the trial, jurors displayed unity by color-coordinating or otherwise matching their attire. It was business attire on one day; sports jerseys on another. Bewildered court observers searched for meaning in the choices.

After the trial, Peterson jurors did not immediately speak to the public, but issued a statement read by Will County Sheriff's Department spokesman Ken Kaupas saying they believe they took their responsibility with "solemnity" and "diligence" and "we have reached a decision that was just."

NBC News staff and Reuters contributed to this report by BJ Lutz of NBCChicago.com.

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