Drew Peterson AP file photo

Peterson was scheduled for arraignment later Friday on charges of first-degree murder in the 2004 death of his third wife, Kathleen Savio, whose body was found in an empty bathtub at home.

Police pulled over Peterson, 55, on Thursday evening shortly after he drove away from his Bolingbrook home. He's in custody in lieu of $20 million bond.

"We are very confident in our case," Will County State's Attorney James Glasgow said.

Peterson will be at the hearing, according to Will County Sheriff's Office spokesman Pat Barry, who said earlier that Peterson would appear via a video hookup. He is being held separately from other inmates at the Will County Adult Detention Facility in Joliet, which is normal with any high-profile case.

"He's also an ex-cop. ... We don't want anybody deciding to pick a fight," Barry said.

Savio's body was found with her hair soaked in blood from a head wound, just before the couple's divorce settlement was finalized. Her death originally was ruled an accidental drowning but authorities later said it was a homicide staged to look like an accident.

The indictment alleges that "Peterson on or about Feb. 29, 2004 ... caused Kathleen Savio to inhale fluid," causing her death.

Savio's family has long voiced suspicions, saying she feared Peterson and told relatives if she died it would not be an accident. Their fears resurfaced after the October 2007 disappearance of Stacy Peterson, then 23.

Drew Peterson is a suspect in the disappearance, which police have called a possible homicide. But he has not been charged and has repeatedly said he thinks Stacy Peterson ran off with another man.

"I guess I should have returned those library books," a handcuffed Peterson said as state police led him into headquarters following his arrest, according to The (Joliet) Herald-News.

Despite the flip comment, "Drew takes these charges very seriously," his lawyer, Joel Brodsky, said Friday on ABC's "Good Morning America." Brodsky said "wisecracks and comedy" are just Peterson's way of dealing with stress.

Glasgow said Thursday that the case against Peterson would include evidence that might previously have been inadmissible. Last year state lawmakers passed legislation that allows a judge to admit hearsay evidence in first-degree murder cases if prosecutors can prove the defendant killed a witness to prevent them from testifying.

"In essence what you're basically allowing the victim of a violent crime to do is testify from the grave," Glasgow said.

Savio filed an order of protection against Peterson in 2002 and in it she wrote that she feared Peterson could kill her.

"He wants me dead and if he has to he will burn the house down just to shut me up," she wrote.

In an interview on Chicago's WGN-TV, Brodsky said he will argue that statements about Peterson made by Savio before her death can't be used by prosecutors in court.

"It's going to have to face a constitutional challenge," he said. "We're now involving rumor and innuendo and unreliable evidence in a homicide case."

Brodsky questioned whether Savio's death was a homicide and said Peterson's $20 million bail is unreasonable.

From the day Stacy Peterson was reported missing, her husband, a cop of nearly 30 years, knew if investigators weren't focused on him, they soon would be. And it wasn't two weeks before the Illinois State Police made it official, calling Peterson a suspect and her disappearance a possible homicide.

Savio's body was found by a friend of Peterson after the police sergeant called him to say he was worried because he had not talked to or seen Savio for a few days. The couple had recently divorced.

Peterson's next wife was Stacy, who was 30 years younger. They had two children, who lived with the couple along with Peterson's two children from his marriage to Savio.

On the morning of Oct. 28, 2007, Stacy Peterson talked to a friend. Stacy's sister, Cassandra Cales, tried to call her in the middle of the afternoon, and did not get through. Late that night, Cales went to Peterson's home, but neither Drew nor Stacy was there. A few minutes later, she reached Peterson on his cellphone, with Peterson telling her that Stacy had left him.

Cales didn't believe it and reported her sister missing the next day.

Pamela Bosco, a friend of Stacy's family who has acted as an unofficial family spokeswoman, said "we're just happy for the Savio family."

"We always said that Stacy and Kathleen had one thing in common ... Drew Peterson," Bosco said.