Gen. David Petraeus let his guard down with Paula Broadwell,

The scandal that brought down CIA Director David Petraeus started with harassing emails sent by his biographer and paramour, Paula Broadwell, to another woman, and eventually led the FBI to discover the affair, U.S. officials told The Associated Press on Saturday.

Petraeus quit Friday after acknowledging an extramarital relationship.

Gen. David H. Petraeus had just assumed his new role as U.S. Central Command chief in 2009 when he began introducing his staff to a young Harvard University researcher who was writing his biography. The woman, Paula Broadwell, then 37, had never written a book and had almost no journalistic experience. But that wasn’t the only thing about her that made the general’s aides nervous.

Petraeus – already the most acclaimed U.S. military commander in recent decades – had until then been extraordinarily careful in managing his public image, allowing limited access to a handful of journalists, former aides say. Yet, when it came to Broadwell, he seemed eager to throw his own rulebook out the window.