Peterson, 58, sat stoically as the verdict was read. He faces a maximum 60-year prison term when sentenced on Nov. 26. Illinois has no death penalty.
The prosecution built its case almost exclusively on circumstantial and hearsay evidence, including testimony about what Peterson's wives had told friends and acquaintances before the one died and the other disappeared. The verdict was a vindication for Will County prosecutors, who gambled by putting on such a case and then committed numerous stumbles during testimony that drew angry scoldings from the judge.
Over the course of the investigation and prosecution, Peterson had seemingly taunted authorities, joking on talk shows and even suggesting a "Win a Date With Drew" contest. His notoriety even inspired a TV movie starring Rob Lowe.
A neighbor found Kathleen Savio's body on March 1, 2004, face down in a dry bathtub of her suburban home outside Chicago. Her thick black hair was blood-soaked and she had a 2-inch gash on the back of her head.
The drowning death of the 40-year-old aspiring nurse was initially deemed an accident - a freak slip in the tub. After Peterson's fourth wife, 23-year-old Stacy Peterson, went missing in 2007 was Savio's body exhumed, re-examined and her death reclassified as a homicide.
Peterson had divorced Savio a year before her death. His motive for killing her, prosecutors said, was fear that a pending settlement, which included their $300,000 home, would wipe him out financially.
Fascination nationwide with the former Bolingbrook police sergeant arose from speculation he sought to parlay three decades of law enforcement expertise into getting away with murder.
Prosecutors suspect he killed his fourth wife because she could finger him for Savio's death. Stacy Peterson's family hoped a conviction in Savio's murder could lead to charges against Drew Peterson in Stacy's disappearance.
Jurors weren't supposed to link the fourth wife's disappearance to the third's death. Prosecutors were prohibited from even telling jurors Stacy Peterson is presumed dead or that her husband is the lone suspect in her disappearance. He says she ran off with another man and is still alive.
Prosecutors faced enormous hurdles.
They had no physical evidence tying Peterson to Savio's death and no witnesses placing him at the scene. They were forced to rely on typically barred hearsay - statements Savio made to others before she died and that Stacy Peterson made before she vanished. In 2008, Illinois passed a law tailored to Peterson's case, dubbed "Drew's Law," permitting hearsay at trials in rare circumstances.
The hearsay included friend Kristen Anderson testifying that Savio told her Peterson once warned her at knife point, "I could kill you and make it look like an accident." Savio so feared for her life that she kept a knife under her mattress.
And Stacy Peterson's pastor, Neil Schori, testified she told him that her husband got up from bed and left their house in the middle of the night around the time of Savio's death. Crying and hugging her knees, she said Drew Peterson later coached her on how to lie to police.
There was damning testimony not based on hearsay.
A former co-worker of Peterson's, Jeff Pachter, testified that Peterson offered him $25,000 to hire a hit man to kill Savio, though he never followed through. After Savio was found dead, Peterson told him, "That favor I asked you - I don't need it anymore."
Prosecutors had to establish the most basic fact for a murder trial: that there was actually a murder.
Pathologists testified for the defense that Savio's wounds indicated an accident. But equally well-respected pathologists for the state said it was impossible for a single fall to cause both the wound on the back of her head and bruises on the front of her body.
In their three-day case, Peterson's lawyers endeavored to cast doubt on the reliability of key witnesses. They accused Savio's sister, Susan Doman, of jazzing up her testimony to profit from a movie and book deal.
The last defense witness was Peterson's and Savio's 19-year-old son, Thomas Peterson. The polite, well-spoken college student cut a sympathetic figure, telling jurors he has never believed his father killed his mom.
Both sides blundered parts of their presentations.
Prosecutors angered the judge several times by broaching subjects previously ruled inadmissible. And as they sought to blunt the credibility of hearsay evidence, the defense ended up prompting their own witness to emphasize that Stacy Peterson was convinced her husband did kill Savio.
Peterson could still win release someday. His lawyers have said they may appeal all the way to the U.S. Supreme Court on grounds Illinois' hearsay law is unconstitutional.
Some legal experts worried about the precedent a conviction at a trial dependent on hearsay would set, saying it could open the floodgates for the admissibility of such evidence in Illinois and elsewhere.