BOLINGBROOK, Illinois (CNN) -- Police are using tracking dogs, airplanes, infrared sensors and volunteers on foot Tuesday to look for a young mother who disappeared nine days ago, leaving her 4- and 2-year-old children behind.
Friends and relatives of Stacy Peterson, 23, say her disappearance is suspicious.
Her husband of four years, Bolingbrook police Sgt. Drew Peterson, 53, reportedly has told police his wife said she was leaving him for another man, and police are not treating the disappearance as a criminal investigation.
But the woman's aunt, Candace Aikin, of El Monte, California, said Stacy Peterson confided in her that there were problems during a visit to the Peterson home in suburban Chicago last month.
"She said that she was afraid because he was following her around 24/7, even inside the house," Aikin said. "He was very obsessed and stalking her, even inside her house.
"She was very, very full of stress and just not happy in her marriage at all," Aikin said. Watch the aunt's impression of the marriage »
Steve Cesare, a friend of Stacy's, said she sent him an e-mail on October 17 saying her husband was "controlling, manipulative and somewhat abusive."
"I knew they had problems," Cesare said. "But the part where it says that he was becoming abusive, that concerned me."
He added, "She wouldn't have left her kids. That's just not going to happen."
Drew Peterson has told police his wife called him from a cell phone late October 28 to say she was leaving him for another man.
"I believe she's not missing. She's where she wants to be," Drew Peterson told The Chicago Sun-Times last week. "I have no reason to suspect foul play."
He told the newspaper, "I believed our marriage was good, but maybe she didn't."
Drew Peterson told the Sun-Times his wife was seeing a psychiatrist, taking anti-depressants and had "mood issues" since the death of her older sister last year from cancer.
But he told the newspaper he found it "very unusual" that Stacy Peterson would leave her children and his kids from a previous marriage whom she had adopted.
"She's a very good mom. For the last year or so, she's been very short-tempered, snapping on everyone, but still a good mom," the Sun-Times quoted Drew Peterson as saying.
CNN has been unable to contact Drew Peterson for comment.
Police are not treating Stacy Peterson's disappearance as a criminal investigation. They say Drew Peterson is cooperating with their investigation. Watch how authorities are searching for the woman »
But local prosecutors are taking another look at the 2004 death of his third wife, Kathleen Savio, who drowned in a bathtub after the couple had divorced.
Savio's sister, Sue Doman, said Savio expressed fear of Drew Peterson.
"She told me all the time, 'He's gonna kill me. It's gonna look like an accident,' " Doman said.
Doman said she didn't believe her sister could have died in the way the investigation concluded.
"I don't understand accidental drowning. You just don't drown in the bathtub, especially a small whirlpool. You just don't do that," she said.
In Illinois on Tuesday, police and volunteers were organizing new search efforts.
State Police Master Sgt. Luis Gutierrez told the Chicago Tribune that investigators were searching nine "areas of interest" using cadaver-sniffing dogs.
The couple's home and a pond at a nearby airport also had been searched, the paper reported.
Investigators told the Sun-Times they also want to talk to the couple's children.
Meanwhile, relatives are clinging to hope.
"I'm still holding on. I'm believing that she's still with us. I'm not going to give up hope at all," Aikin said. E-mail to a friend