(CNN) -- An Illinois jury on Thursday found former Chicago-area police sergeant Drew Peterson guilty of murder in the 2004 death of his ex-wife.
The jury of seven men and five women deliberated for nearly 14 hours total before delivering its verdict convicting Peterson in the death of his third wife, Kathleen Savio.
"Finally somebody heard Kathleen's cry," her mother, Marcia Savio, told reporters after the verdict. "Twelve people did the right thing, oh thank God."
Savio was found dead in her dry, clean bathtub on March 1, 2004.
While prosecutors claimed Peterson killed Savio, the defense contended that she fell, hit her head and drowned.
The headline-grabbing case did not arise until after Peterson's fourth wife, Stacy, disappeared in October 2007. It was during the search for Stacy Peterson -- who has not been found -- that investigators said they would look again into Savio's death, which was initially ruled an accidental drowning.
In February 2008, authorities altered their judgment and ruled Savio's death a homicide. Peterson was later arrested and charged with first-degree murder.
Peterson was married to Savio in 2001 when he had an affair with then-17-year-old Stacy Cales, who later became his fourth wife. Savio and Peterson filed for divorce in October 2001 and their relationship remained contentious for the next several years.
Bolingbrook, Illinois, police records indicate officers were called to Savio's home 18 times to intervene in domestic fights from 2002 to 2004. Peterson had Savio arrested twice for domestic violence, though she was found not guilty in both cases.
On February 27, 2004, Peterson picked up his two sons from Savio's home and spent the next two days with them. Prosecutors said he entered her home again early on February 29 and killed her.
At the time of her death, a court was mulling how the couple's marital assets would be divided, and Savio was set to receive part of Peterson's pension and other support.
"We have left-front injuries, left-side injuries, left-back injuries, right injuries, right and left injuries," prosecutor Chris Koch said in his closing argument, disputing the defense assertion Savio's death was an accident. "So it's not just one side of her body; it's multiple sides, four sides.
"How can you get that in one fall? You can't. You can't do it. It's not possible."
The jury released a statement, read outside the Joliet courthouse by Will County Sheriff's Office Deputy Ken Kaupas, in which they thanked the judge, bailiffs and sheriff's office and said they took their responsibility seriously.
"We have reached a decision we believe is just," the jurors said.
The more-than-monthlong trial was marked by repeated missteps by the prosecution that angered Judge Edward Burmila and the defense.
At least four times, prosecutors allowed witnesses to testify to details Burmila had told them not to go into -- such as whether Savio had a protective order against her husband or allowing a witness to demonstrate climbing into a bathtub.
In some cases the defense sought a mistrial and in others they asked the judge to strike entire testimony. Burmila instead ordered the jury to disregard elements of the testimony that went against his orders.
"The disrespect to the court is shocking," Burmila told the prosecution last week.
On Thursday, Will County State's Attorney James Glasgow expressed confidence the conviction, which he called "very sobering," will stand up against appeal.
"We took him on and we won," he said of Peterson, whom he called "a coward and a bully."
"This defendant brutally killed Kathleen Savio."
After Thursday's verdict, Peterson's defense team stood by their client and promised to continue their fight on his behalf. Lawyer Joel Brodsky contended there was a large amount of bias against Peterson before the trial even began.
"He is absolutely innocent," Brodsky said of Peterson, claiming the prosecution's case "was based almost entirely on hearsay." He called Savio's death "a household accident."
The Savio family, though, didn't hide their contempt for what the victim's brother, Nick, called Peterson's "clown defense team who made fun of this whole trial."
Nick Savio called Thursday's verdict "bittersweet," describing the jury's decision as "fantastic" while also lamenting it wouldn't bring back his sister. He added that his family wants Drew Peterson to next be held responsible for whatever happened to Stacy Peterson.
"Although we cannot have Kathleen back, we hope she can now rest in peace and that she knows she has had her day," Nick Savio said, reading out a statement from family. "She will be missed and remembered in our hearts always.
"Stacy, you are now next for justice."
Cassandra Cales, Stacy Peterson's sister, said she hopes the verdict will spur someone to come forward "who knows something about my sister, (because) they feel safe to talk now."
While she says she is still trying to process the import of the jury's decision, Cales said one thought went through her mind immediately after hearing it: "Game over, Drew."
InSession's Michael Christian contributed to this report.