CHICAGO (CBS) — The search for more possible victims of serial killer John Wayne Gacy is now in the hands of the FBI.

WBBM Newsradio’s Steve Miller reports the Cook County Sheriff’s office has turned over Gacy’s travel records to the FBI, which will check for matches in unsolved murders across the country while Gacy was killing at least 33 boys and young men.

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“They input all that information, and they take it and lay it over all of the unsolved homicides and missing person cases that occurred in the entire United States during that period of time,” Cook County Sheriff Tom Dart said. “Then they see if there’s any matches showing Gacy in a town at the time that a body was found.”

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Dart confirmed a dig on the Northwest Side property where Gacy’s mother lived has not turned up any human remains.

“We’ll have a definitive answer next week, but … every indication right now points to the fact that there’s nothing out there,” Dart said.

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Dart said three sets of DNA – from three families – are now at the lab to see if they match any of the remains of the seven still-unidentified Gacy victims.