The day-long search in a Shorewood forest preserve by boat, by helicopter and by foot with dogs on Monday was for Drew Peterson's missing wife Stacy, according to law enforcement sources.
Stacy Peterson, 23, disappeared in Oct. 2007. She was Peterson's fourth wife.
The search in the Hammel Woods area is not related to any new leads, but is part of periodic searches held in the case, according to the source.
The Illinois State Police was assisted on Monday by the FBI. Neither agency would speak officially about the operation -- except to say it was part of an ongoing criminal investigation.
Peterson is considered a suspect in Stacy's disappearance, but has not been charged.
The former Bolingbrook police sergeant is behind bars; Peterson was convicted of killing his third wife, Kathleen Savio, two months ago.