The investigation into why Berger illegally sneaked top-secret documents out of the archives has been quietly progressing for months. At the time Berger was Democratic presidential nominee John F. Kerry's top foreign policy adviser.
"It may have been off the front pages, but the investigation has been active," said a source told the Post.
Berger admitted he removed as many as 50 top-secret documents from the archives, calling it an an "honest mistake" made while he vetted documents for the Sept. 11 commission's inquiry into the terror attacks on New York and Washington. He also acknowledged he destroyed some documents, but claimed it was by accident.
The pilfered documents were classified "Code Word," the highest security classification, above Top Secret.
Some Republicans, including House Speaker J. Dennis Hastert, R-Ill., have charged the documents were taken because they might embarrass the former president.
The investigation, which has been characterized as "a criminal probe," is being conducted by career prosecutors at the Justice Department, sources said.