a simple e-mail cybertrail, his undoing.artha raddatz has the latest. >> reporter: when general david petraeus granted paula broadwell exclusive and extraordinary access to pen his biography, he likely never imagined it would lead to his downfall. but tonight, his reputation is solid, the fbi is under scrutiny and agents have descended on broadwell's home to gather more material. material broadwell is now willingly providing them in this increasingly strange scandal. the affair first came to light this summer as part of an fbi investigation prompted by a complaint from this woman, jill kelly, a private citizen and military supporter who had befriended petraeus and his wife holly. kelly received harassing e-mails from an anonymous account and took them to a friend at the fbi in may or june. the bureau obtained a court order and electronically traced the accounts to petraeus' biographer. broadwell eventually turned her computer over to the fbi. they were stunned to discover hundreds if not thousands of e-mails some salacious b