The plot surrounding the resignation of CIA chief David Petraeus over an extramarital affair thickened on Sunday with reports that his alleged lover had sent emails to a second woman seen as a threat to her love interest.
The affair came to light as the FBI was investigating whether a computer used by Petraeus -- the celebrated ex-US commander in Iraq and Afghanistan -- had been compromised, the New York Times and other US media reported, citing government officials.
NBC News and others have reported the Federal Bureau of Investigation was focusing on Paula Broadwell, co-author of a favorable biography of Petraeus, for possible improper access to classified information.
Unnamed officials told the Times that Petraeus's lover was Broadwell, a former Army major who spent long periods interviewing Petraeus for her book.
Broadwell has offered no public comment on the revelations.
The Times and The Washington Post, citing an official briefed on the case, said on Saturday that the probe had been triggered by 'harassing' emails sent by Broadwell to an unidentified second woman.
The recipient of the emails was so frightened, according to the Post, that she went to the FBI for protection and to help track down the sender.
According to the Post, the second woman did not work at the Central Intelligence Agency and her relationship with Petraeus remains unclear. However, the emails indicated that Broadwell perceived her as a threat to her relationship with the top US spymaster, the paper said.
Broadwell, a counterterrorism expert, lives in Charlotte, North Carolina, with her husband Scott Broadwell, a local radiologist, and their two young sons.
She is said to be well known in the city through her volunteer work to raise money for wounded soldier organizations.
Broadwell reportedly planned to celebrate her 40th birthday at a big party in Washington this weekend. But late Friday, her husband emailed guests to cancel the invitations.
President Barack Obama had no inkling Petraeus, 60, was about to leave until Thursday morning and refused to accept his resignation straight away, according to the Times.
"He was surprised, and he was disappointed," the newspaper quoted one senior administration official as saying. "You don't expect to hear that the Thursday after you were re-elected."
A senior intelligence official told the Times that US director of national intelligence James Clapper learned of the situation on Tuesday and had told Petraeus that "the right thing to do" would be to resign.
As he heads into his second term, besides picking a new CIA chief, Obama will likely have to replace not only departing Secretary of State Hillary Clinton, but also defense secretary Leon Panetta and treasury secretary Tim Geithner.
Speculation is already rife about who will succeed Clinton, who has stressed she wants to reclaim a private life put on hold by decades in the spotlight.
Search for Replacement Expected to Be Daunting
Now the rumor mill is spinning with talk of who might follow in the footsteps of Petraeus, a former paratrooper and retired four-star general credited with turning around the Iraq war.
His deputy Michael Morell will serve as acting CIA director, and is expected to fill in for Petraeus at an upcoming congressional hearing about the CIA's alleged failure to protect a US consulate in Libya from a deadly September 11 attack that killed four Americans, including Ambassador Chris Stevens.
One name being floated as a possible Petraeus replacement is John Brennan, the White House counter-terrorism adviser and a CIA veteran who has played an instrumental role in Obama's drone war against Al-Qaeda militants.
Others, according to the Wall Street Journal, include Michael Vickers, undersecretary of defense for intelligence, and Congressman Michael Rogers, a Republican who heads the House Permanent Select Committee on Intelligence.
"It needs to be someone who has a lot of credibility... and doesn't have a partisan reputation," Georgetown University professor Stephen Wayne told AFP.
Wayne also floated the name of former Republican senator Chuck Hagel but said his guess would be that Morell will stay put permanently if he does well in the interim.
The most celebrated military officer of his generation, Petraeus took over at the CIA a little more than a year ago. He was credited by some with rescuing a failing US war effort in Iraq in 2007, after then president George W. Bush ordered a surge of troops into the country.
Obama later asked Petraeus to lead a similar surge of US forces in Afghanistan in 2010, leaving a top post as commander of all US forces in the Middle East to do so.
His military background, however, sometimes clashed with the CIA's culture and there was some friction with the congressional committees that oversee the spy services.
In this case, however, the extramarital liaison raises potential security concerns in light of Petraeus's highly sensitive position.
He himself said in a message to CIA staff, released to the media Friday, that "such behavior is unacceptable, both as a husband and as the leader of an organization such as ours."
Still, Foreign Policy in a blog post called his downfall a "huge loss for the United States."
"Petraeus's exit leaves a bitter taste. We all make mistakes. Here's hoping he makes a comeback," the journal said.