Joliet, Illinois (CNN) -- Attorneys for Drew Peterson, a former Chicago-area police officer accused of murdering his third wife, argued during opening statements Tuesday that their client spent his career protecting the public and that murder accusations are groundless.
"Kathy slipped, fell, hit her head in a household accident, and drowned. Case closed," said attorney Joel Brodsky.
Kathleen Savio was found dead in a bathtub in 2004. Peterson also remains under investigation in the October 2007 disappearance of his fourth wife, Stacy Peterson.
Prosecutors, meanwhile, argued that Peterson was motivated to kill, at least in part, by his desire to avoid settlement payments to his ex-wife.
"This (is) not a case where you'll have DNA, fingerprints, or a videotaped confession . . . (But) when you've heard all the evidence, you'll be able to determine that Drew Peterson killed Kathleen Savio beyond a reasonable doubt," said Will Country State's Attorney James Glasgow during his opening statement.
Prosecutors called Mary Pontarelli, a neighbor, as their first witness. Her voice cracked on a couple of occasions as she described finding the body of Savio, her friend.
Court is scheduled to resume Wednesday morning.
A jury of seven men and five women, chosen over two days last week, will decide Drew Peterson's fate during the trial in Joliet, Illinois, which is expected to last about a month, according to his lawyer.
Peterson, 58, was married to Savio in 2001 when he had an affair with then-17-year-old Stacy Kales, who later became Stacy Peterson.
Savio and Peterson filed for divorce that October, 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. Drew Peterson had Savio arrested twice for domestic violence, though she was found not guilty in both cases.
A judge in March 2002 granted Savio a protection order from her ex-husband, prohibiting him from being near her, entering her home or taking out their children except for two brief weekly visits.
Savio had claimed that months later, Peterson held a knife to her throat and threatened to kill her inside her home.
On February 27, 2004, Drew Peterson picked up his two sons from Savio's home, spending the next two days with them.
Prosecutors believe that he entered her home again early on February 29 and killed Savio; she was found naked and dead in her dry tub the next day.
At the time of her death, a court was mulling how their marital assets would be divided, and Savio was set to receive part of Peterson's pension and other support.
Police initially treated the scene as an accident, although the Illinois State Police was later brought in to investigate.
Peterson's trial had been set to start in July 2010 but was delayed.
In April, an Illinois appellate court ruled that prosecutors may use potentially incriminating statements made by Savio and Drew Peterson's still-missing wife Stacy against him, a key development in the case.
The ruling overturned an earlier judge's decision that forbade prosecutors from using eight statements made by Savio before her death and by Stacy Peterson before her disappearance. The defense had argued that using the statements would violate Drew Peterson's right to confront the witnesses against him.