By late summer, after the monitoring of Ms. Broadwell’s emails uncovered the link to Mr. Petraeus, prosecutors and agents alerted senior officials at FBI and the Justice Department, including Mr. Holder, U.S. officials say. The investigators never monitored Mr. Petraeus’s email accounts, the officials say…

On her computer, investigators found classified documents, the U.S. officials said, a discovery that raised new concerns.

At Mr. Petraeus’s interview in the week before the election, he also admitted the affair and said he hadn’t provided the classified documents to Ms. Broadwell. Agents conducted a second interview with Ms. Broadwell on Nov. 2. She also said Mr. Petraeus wasn’t the source of the documents…

U.S. officials briefed on the matter said the probe was closely held among officials at the FBI and Justice under a long-standing policy not to divulge information on continuing criminal investigations.

The disclosure policy was reinforced in a 2007 memorandum by Michael Mukasey, who was then attorney general under President George W. Bush. The memorandum, issued in the wake of the scandal over the firings of U.S. attorneys, sought to remind department employees that contacts with the White House and Congress about pending criminal matters were off limits.