Meanwhile, the F.B.I. agent who had helped get a preliminary inquiry started, and learned of Mr. Petraeus’s affair and the initial concerns about security breaches, became frustrated. Apparently unaware that those concerns were largely resolved, the agent alerted the office of Representative Eric Cantor, Republican of Virginia, the House majority leader, about the inquiry in late October. Mr. Cantor passed on the agent’s concerns to Mr. Mueller.
http://www.nytimes.com/2012/11/12/us/us-officials-say-petraeuss-affair-known-in-summer.html?pagewanted=all&_r=1&