Drew Peterson was arrested Thursday on charges he murdered his third wife

Drew Peterson was arrested Thursday on charges he murdered his third wife, the biggest development yet in the case against the former Chicago-area police sergeant — who shot into the national spotlight after the suspicious disappearance in October 2007 of his fourth wife, Stacy Peterson.

Former police sergeant Drew Peterson, long suspected in the 2007 disappearance of his fourth wife, was charged Thursday with murdering his third wife, whose 2004 death had been deemed accidental before authorities revisited it once Stacy Peterson vanished.

Will County prosecutors and Illinois State Police planned an evening news conference to discuss a murder indictment issued against the former Bolingbrook police officer in the death of Kathleen Savio.

Peterson was arrested Thursday evening during a traffic stop in Bolingbrook, said Chuck Pelkie, spokesman for Will County state's attorney.

Peterson was alone in his car at the time.

State police later searched Peterson's home, MyFOXChicago.com reported.

Peterson's attorney told FOX News that he was unaware of the arrest.

Peterson has been a suspect in the disappearance of his 23-year-old wife Stacy Peterson, who vanished on Oct. 28, 2007, from her Bolingbrook, Ill., home.

In the months following Stacy Peterson's disappearance, Savio's body was exhumed and her 2004 bathtub drowning death was re-classified as a homicide.

Nick Savio, Kathleen's brother, told ABC 7 state police informed his sister Susan that Peterson was arrested on Thursday.

Pam Bosco, spokesperson for Stacy Peterson's family, told ABC 7 that the arrest was long anticipated by the family.

Martin Glink, the Savio family's attorney, said the family hoped Peterson would be charged.

Savio's family filed a wrongful death lawsuit last month, alleging Peterson downed her in the bathtub.

Kathleen Savio's family has long voiced suspicions about the circumstances surrounding her 2004 death, especially following the disappearance of Peterson's fourth wife, Stacy.

The lawsuit seeks more than $100,000 and alleges Peterson killed Savio before a scheduled trial over the divorced couple's property.

The lawsuit alleges Peterson went to Savio's house on Feb. 28, 2004, to "brutally ... stalk, attack, repeatedly beat, then drown, decedent Kathleen Savio."

Authorities declined to immediately release further details.

Savio's body was found in an empty bathtub. Savio's family has long voiced suspicions about the circumstances surrounding her death, especially after the October 2007 disappearance of Stacy Peterson, then 23.

Peterson, 55, is a suspect in the disappearance but has not been charged in that case. He has repeatedly said he thinks Stacy Peterson ran off with another man.

Peterson's attorney, Joel Brodsky, said in an e-mail Thursday he was on his way to New York and referred messages to Peterson's publicist, Glenn Selig. Selig said only that he could not confirm Peterson's arrest.

An HBO spokeswoman said the network would sooner cancel the show than allow Peterson to appear on it.