Even when he was first arrested Thursday, he joked, "I guess I should have returned those library books."
"He's an idiot," Susan Doman, Savio's sister, said today on "Good Morning America," dismayed that Peterson would make jokes after he was arrested for his wife's murder.
A judge postponed Peterson's arraignment until May 18 because neither of Peterson's attorneys were in court today, The Associated Press reported. Peterson didn't speak in court except to tell the judge he understood the continuance. He's being held on $20 million bond.
The indictment's legal language accuses Peterson of drowning Savio, saying that he forced her to "inhale fluid" and that he did it "with the intent to kill Kathleen Savio."
Savio's sister, Susan Doman, said the world is finally a "safe place for me" now that Peterson has been arrested.
Stacy Peterson's friends and family said last week that her husband's arrest is bittersweet.
"It's a very hollow victory right now not knowing where Stacy is," said Sharon Bychowski, a friend of Stacy Peterson who lives next door to Drew Peterson. "We still have a ways to go. It wasn't quite the victory I thought it would be."
Pam Bosco, a friend and family spokesman, said the family "understands that it's ongoing and we just have to be patient with it."
Peterson has maintained his innocence to anyone who would listen both in Savio's death and Stacy Peterson's disappearance. At times he's even seemed to revel in the spotlight.
"Drew takes these charges very seriously," his lawyer Joel Brodsky told "Good Morning America." Those jokes, he said, are his way of dealing with stress. "That's just his nature."
Doman said the family hopes the arrest is the first step in justice for her sister. Peterson was arrested shortly before he was scheduled to fly to Reno to interview for a security job at a brothel featured on a cable television show.
"It was a big relief because he wasn't going on all these shows, going around joking and laughing," Doman said.
Andrew Abood, an attorney for Peterson, told The Associated Press the indictment was not a surprise because "there was tremendous pressure for the government to do something in this case."
He added Peterson had a "lock-tight alibi" because Peterson and Savio's teenage son said last month in a television interview that he was with his father at the time of his mother's death.
"I highly do not believe that my dad had murdered my mom," Thomas Peterson, 16, told CBS' "The Early Show." "Because, first off, he wasn't there. He was with us during that period of time."
Peterson, a former duty sergeant for the Bolingbrook Police Department, was the first officer to respond to the scene of Savio's death. His nearly-three-decade career in law enforcement ended when he stepped down after Stacy Peterson disappeared.
Brodsky said he had not spoken with his client as of late Thursday night, but expected to speak with him Friday.
The Associated Press contributed to this story.