WASHINGTON (AP) ― 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.

The identity of the other woman and her connection with Broadwell were not immediately known.

Concerned that the emails he exchanged with Broadwell raised the possibility of a security breach, the FBI brought the matter up with Petraeus directly, according to the official, who spoke on condition of anonymity because he was not authorized to publicly discuss the investigation. The FBI approached the CIA director because his emails in the matter were in most instances sent from a personal account, not his CIA one.

Petraeus decided to quit, abruptly ending a high-profile career that might have culminated with a run for the presidency, a notion he was believed to be considering.

“Such behavior is unacceptable, both as a husband and as the leader of an organization such as ours,” Petraeus wrote his staff.

Petraeus handed his resignation letter to President Barack Obama on Thursday, stunning many in the White House, the CIA and Congress. The news broke in the media before the House and Senate intelligence committees had been briefed, officials say.

By Friday evening, multiple officials identified Broadwell, who spent the better part of a year reporting on Petraeus’ time in Afghanistan.

Members of Congress said they want answers to questions about the affair that led to Petraeus’s resignation.

House intelligence committee chairman Mike Rogers and ranking Democratic member Dutch Ruppersberger will meet Wednesday with FBI deputy director Sean Joyce and CIA acting director Michael Morell to ask questions, including how the investigation came about, according to a senior congressional staffer who spoke anonymously because he was not authorized to discuss the investigation publicly.

Petraeus has been married for 38 years to Holly Petraeus, the daughter of the West Point superintendent when he was a student at the New York school.

“He is truly remorseful about everything that’s happened,’’ said Steve Boylan, a retired army officer and former Petraeus spokesman who spoke with the former general on Saturday. In a phone call with Boylan Saturday, Petraeus lamented the damage he’d done to his “wonderful family” and the hurt he’d caused his wife.

“He screwed up, he knows he screwed up, now he’s got to try to get past this with his family and heal,” said Boylan.

Broadwell interviewed the general and his close associates intensively for more than a year to produce the best-selling biography, “All In: The Education of General David Petraeus,” which was written with Vernon Loeb, a Washington Post editor, and published in January. Since Petraeus’s resignation on Friday, the book jumped from a ranking on Amazon of 76,792 on Friday to 111 by mid-Saturday

The CIA was not commenting on the identity of the woman with whom Petraeus was involved.

Broadwell, who is married with two young sons, has not responded to multiple emails and phone messages. Broadwell planned to celebrate her 40th birthday party in Washington this weekend, with many reporters invited. But her husband emailed guests to cancel the event late Friday.

CIA officers long had expressed concern about Broadwell’s unprecedented access to the director. She frequently visited the spy agency’s headquarters in Langley, Virginia, to meet Petraeus in his office, accompanied him on his punishing morning runs around the CIA grounds and often attended public functions as his guest, according to two former intelligence officials.

As a military intelligence officer in the Army Reserve, Broadwell had a high security clearance, which she mentioned at public events as one of the reasons she was well suited to write Petraeus’s story.

But her access was unsettling to members of the secretive and compartmentalized intelligence agency, where husbands and wives often work in different divisions, but share nothing with each other when they come home because they don’t “need to know.’’

In one incident that caught CIA staff by surprise, Broadwell posted a photograph on her Facebook page of Petraeus with actress Angelina Jolie, taken in his 7th floor office where only the official CIA photographer is permitted to take photos. Petraeus had apparently given Broadwell the photo just hours after it was taken.

Petraeus’ staff in Afghanistan similarly had been concerned about the time Broadwell spent with their boss on her multiple reporting visits to the war zone. Following standard military procedure with senior officers, they always had another staffer present when she met with him at his headquarters. Military officers close to him insist the affair did not begin when he was in uniform.

In the preface to her book, Broadwell said she first met Petraeus in the spring of 2006. She was a graduate student at the Kennedy School of Government at Harvard; he was visiting the university to discuss his experiences in Iraq and a new counterinsurgency manual he was working on.