WASHINGTON – 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.

The official said the FBI investigation began several months ago with a complaint against Broadwell, a 40-year-old graduate of the U.S. Military Academy and an Army Reserve officer. That probe led agents to her email account, which uncovered the relationship with the 60-year-old retired four-star general, who earned acclaim for his leadership of the wars in Iraq and Afghanistan.