Former national security adviser Sandy Berger has resigned from his post as an advisor to Democratic presidential candidate John Kerry. This follows the revelation this week that Berger is under criminal investigation by the Justice Department over allegations that he took secret documents from the National Archives while reviewing Clinton administration records for the 9/11 commission. Sources said that among the documents Berger took were drafts of a Clinton administration “after-action” report on efforts to thwart the so-called “millennium plot,” a suspected al Qaeda attack planned around the New Year’s holiday in 1999. Berger said in a statement Monday that the removal of the papers was unintentional.

In a brief statement to reporters Tuesday night, Berger said that while reviewing documents last year he “made an honest mistake. It is one that I deeply regret.” He said any suggestion that he had done anything other than try to aid the 9/11 commission “is simply, absolutely wrong.” Law enforcement sources said archive staff members told FBI agents they saw Berger placing items in his jacket and pants, and one archive staffer told agents that Berger also placed something in his socks. That latter allegation drew a sharp response from Berger associate and former White House lawyer Lanny Davis, who challenged any unnamed official who makes such an accusation to come forward publicly. Davis said “I suggest that person is lying. And if that person has the guts, let’s see who it is who made the comment that Sandy Berger stuffed something into his socks.”

Berger was designated as the official from the Clinton administration who would review documents relevant to 9/11 commission inquiries into the terrorist attacks of September 11, 2001. He also was a witness at commission hearings and reviewed records to prepare for his personal testimony.