WASHINGTON (Reuters) - The FBI investigation that led to the discovery of CIA Director David Petraeus' affair with author Paula Broadwell was sparked by "suspicious emails" from her to another woman and Petraeus was not the target of the probe, U.S. law enforcement and security officials told Reuters on Saturday.
But the CIA director's name unexpectedly turned up in the course of the investigation, two officials and two other sources briefed on the matter said.
The FBI was looking into "an issue with two women and they stumbled across the affair with Petraeus," a U.S. government security source said.
The FBI probe was triggered when Broadwell sent threatening emails to an unidentified woman close to the CIA director, a security official said, speaking on condition of anonymity. It was unclear what the relationship of the woman who received the emails was to Petraeus.
The woman went to the FBI complaining of cyber harassment and the law enforcement agency traced the threats to Broadwell, the security official said. The FBI then uncovered explicit emails between Petraeus and Broadwell, The Washington Post reported.
Attempts by Reuters and other news media to reach Broadwell, an Army reserve officer and author of a biography of Petraeus, have not been successful.
The FBI and CIA declined comment on Saturday.
Many questions in the case remain unanswered publicly, including the identity of the second woman; the precise nature of the emails that launched the FBI investigation; and whether U.S. security was compromised in any way.
Nor is it clear why the FBI waited until Election Day to tell Director of National Intelligence James Clapper, who oversees the CIA and other intelligence agencies, about its investigation involving Petraeus.
In attempting to explain the time between Petraeus' FBI interview two weeks earlier and the DNI's notification on Election Day, the security official said there had been no evidence any crime had been committed.
The CIA director announced his resignation suddenly on Friday, acknowledging an extramarital affair and saying he showed "extremely poor judgment.
The developments likely ended the public career of one of the United States' most highly regarded generals, who was credited with helping pull Iraq out of civil war and led U.S. and NATO troops in Afghanistan.
New details emerged on Saturday about developments in the final days leading to Petraeus' departure from atop the CIA.
Clapper was notified by the FBI on Tuesday evening about 5 p.m. - just as returns in the U.S. presidential election were about to come in - about "the situation involving Director Petraeus," a senior intelligence official said. Clapper and Petraeus then spoke that evening and the following morning.
"Director Clapper, as a friend and a colleague and a fellow general officer, advised Director Petraeus that he should do the right thing and he should step down," the official said.
Clapper is a retired Air Force lieutenant general; Petraeus served nearly four decades in the U.S. Army and retired as a four-star general.
On Wednesday, Clapper notified the National Security Council at the White House that Petraeus was considering resigning and President Barack Obama should be informed, the official said.
U.S. law enforcement, security and intelligence officials agreed to discuss the Petraeus matter only on condition of anonymity because of the issue's sensitivity and because it is the subject of a law enforcement investigation.
Once Petraeus' name turned up in the investigation, the importance of the FBI inquiry was immediately escalated, as investigators became concerned the CIA chief somehow might have been compromised, the law enforcement official said.
However, the official and two sources briefed on the matter said no evidence has turned up suggesting Petraeus had become vulnerable to espionage or blackmail. At this point, it appears unlikely that anyone will be charged with a crime as a result of the investigation, the official said.
The FBI investigation began fairly recently - months rather than years ago, when Petraeus would still have been in uniform as one of the U.S. Army's top field commanders, the official said.
Representative Peter King, Republican chairman of the House of Representatives' Homeland Security Committee, said in an interview on MSNBC: "It's hard to believe this went on for four or five months at this level without the president or somebody in the White House being told about it by the FBI. I would have thought the FBI had an absolute obligation to tell the president when this type of investigation is going on."
"And then we're told the White House was told about it the very day after the election is (over). It raises a lot of questions. I'm not into conspiracy theories but this one just doesn't add up," said King, who is a frequent critic of the White House.
FBI Deputy Director Sean Joyce and acting CIA Director Michael Morell will separately brief the chairman and top Democrat of the House intelligence committee on Wednesday about Petraeus, a committee aide told Reuters.
House Intelligence Committee Chairman Mike Rogers, a Republican, is "very concerned and has got a lot of questions," the aide said.
Several officials briefed on the matter said senior officials at the Pentagon, CIA and Congress knew nothing of the FBI's investigation of Petraeus until Thursday afternoon at the earliest, and some key officials were not briefed on the details until Friday.
There is no evidence at this time that anyone at the White House had knowledge of the situation involving Petraeus prior to the U.S. presidential election on Tuesday, which saw Obama elected to a second four-year term.
Another U.S. government security source said it was not until Friday afternoon that some members of the House and Senate intelligence oversight committees were notified about Petraeus' resignation by Clapper's office.
The congressional committees were told that it was a personal issue that Petraeus had to discuss with his wife. When pressed, a representative of the Office of the Director of National Intelligence said it involved another woman. (Writing by Warren Strobel; Additional reporting by Doug Palmer and Matt Spetalnick; Editing by Todd Eastham and Eric Walsh)