See the report below from an FNC colleague (and note the screen grab from biographer Paula Broadwell’s appearance on THE DAILY SHOW to promote the biography of Petreaus):
We can report the following:
The Petraeus affair with his biographer Paula Broadwell was revealed in the course of an FBI investigation. The FBI was investigating a much broader case – unrelated to any of this – and in the course of that investigation Broadwell’s name came up. The FBI followed that lead, and in doing so then Petraeus’ name came up. The FBI for some time was concerned that perhaps Petraeus was some sort of victim or that there may have been some sort of security breach (on Broadwell’s part), but there has been no evidence discovered to back up such concerns.