CHICAGO (AP) — The FBI will join the search for the wife of a former suburban police sergeant, whom authorities have called a suspect in her disappearance nearly a month ago, a spokesman for the federal agency said Saturday.

The FBI's involvement comes at the request of the Illinois State Police, which is leading the investigation into the disappearance of Stacy Peterson, 23, from the couple's home.

The case has led prosecutors to re-examine the 2004 death of Drew Peterson's third wife, Kathleen Savio. Authorities have said her death may have been a homicide staged to look like an accidental drowning.

Savio's body was exhumed for a new autopsy. The state's attorney's office said it could be a couple weeks before investigators have results from tests on her remains.

Peterson, 53, who has not been called a suspect in Savio's case, has denied any wrongdoing in her death and has proclaimed his innocence in Stacy Peterson's disappearance.