A prosecutor's spokesman says the FBI has been asked to join the search for Stacy Peterson.

Charles Pelkie, a spokesman for the Will County state's attorney, says the FBI's involvement would make it possible for the U.S. Navy to provide technical assistance.

It has been four weeks since 23-year-old wife of former Bolingbrook police sergeant Drew Peterson vanished. Authorities have said they believe the 2004 death of Peterson's third wife, Kathleen Savio, was a homicide staged to look like an accidental drowning.

Peterson has not been called a suspect in Savio's death, but authorities have said they suspect him in Stacy Peterson's disappearance.