FBI probe of CIA chief David Petraeus's emails led to affair discovery – reports

New details have emerged over the shock resignation of CIA chief David Petraeus, suggesting that the chain of events leading to his eventual downfall began with an FBI probe into his personal email account.

Several American news organisations reported that investigators began monitoring Petraeus's email after it was alerted that his biographer, Paula Broadwell, may have had access to his messages.

In the course of that investigation it was discovered that Petraeus and Broadwell were having an extramarital relationship. The clandestine affair led to this spy chief's sudden resignation on Friday, just a week before he was due to testify at hearings into the death of the US ambassador to Libya in an attack on the consulate in Benghazi. Petraeus is now no longer expected to appear.

Broadwell allegedly sent "harassing emails" to another woman. The unnamed second woman complained, sparking a security investigation. Broadwell suspected the other woman was in a relationship with the CIA chief, the Journal said, citing sources inside the investigation. There is no evidence Broadwell's suspicions were true, it added.

Nonetheless, the CIA chief's downfall seems to have come about come about as a result of a possibly romantic imbroglio involving two different women. The FBI and prosecutors in Florida and North Carolina began investigating the possibility of email hacking, since some of the emails sent by Broadwell contained contents of messages that appeared to come from Petraeus's private Gmail account, it was reported.

In stepping down, the four-star general said he had shown "extremely poor judgment" by having an extramarital affair. It was an embarrassing fall from grace for one of America's most senior and respected military thinkers, who was one of the most high-profile members of the Obama administration.

Petraeus, who went to see President Obama on Thursday, to offer his resignation, said in a letter published on Friday that he had resigned for personal reasons.

"After being married for over 37 years, I showed extremely poor judgment by engaging in an extra-marital affair," he said in the letter. "Such behaviour is unacceptable, both as a husband and as the leader of an organisation such as ours."

Petraeus met his wife, Holly, when he was a cadet at West Point, of which her father was the superintendent at the time. Mrs Petraeus is an official with the Consumer Financial Protection Bureau, working with the office of service member affairs, which looks after the financial interests of those serving in the military.

The deputy CIA director, Michael Morell, an Asia specialist, is to take over the running of the agency in the short term, on the understanding that Obama will nominate him for the director position on a permanent basis. The nomination must be formally approved by the Senate.

In his statement, addressed to colleagues, Petraeus said: "As I depart Langley, I want you to know that it has been the greatest of privileges to have served with you, the officers of our nation's Silent Service, a workforce that is truly exceptional in every regard. Indeed, you did extraordinary work on a host of critical missions during my time as director, and I am deeply grateful to you for that.

"Teddy Roosevelt once observed that life's greatest gift is the opportunity to work hard at work worth doing. I will always treasure my opportunity to have done that with you and I will always regret the circumstances that brought that work with you to an end."

Obama issued a statement, praising Petraeus for what it called "extraordinary service" to the US for decades.

"By any measure, he was one of the outstanding general officers of his generation, helping our military adapt to new challenges, and leading our men and women in uniform through a remarkable period of service in Iraq and Afghanistan, where he helped our nation put those wars on a path to a responsible end," the president's statement said.

"As director of the Central Intelligence Agency, he has continued to serve with characteristic intellectual rigor, dedication, and patriotism. By any measure, through his lifetime of service David Petraeus has made our country safer and stronger."

Obama added: "My thoughts and prayers are with Dave and Holly Petraeus, who has done so much to help military families through her own work. I wish them the very best at this difficult time."

James Clapper, the director of national intelligence, said in a statement: "Dave's decision to step down represents the loss of one of our nation's most respected public servants. From his long, illustrious Army career to his leadership at the helm of CIA, Dave has redefined what it means to serve and sacrifice for one's country."

After news of the resignation broke, on NBC, it emerged that Petraeus would no longer have to testify before a congressional hearing next week, regarding the Benghazi consulate attack. This prompted speculation that his departure was also connected to criticism of the CIA's handling of the issue. But as the details of the FBI investigation and the possible security breach emerged on Friday night, this seemed unlikely.

A glittering military career

Petraeus took up the CIA post in September 2011, after what was regarded in Washington as a glittering military career. He was credited with crafting – after listening to younger officers – the counter-insurgency strategy in Iraq that helped the US beat al-Qaida with the help of Sunnis.

Afghanistan was more difficult but again he was given credit in Washington for having done a good job, given all the problems stacked against him.

He was frequently tipped in Washington circles as a potential Republican presidential candidate.

Senator John McCain, a champion of Petraeus down the years but now one of the leading critics of the administration's handling of Benghazi, issued a statement praising the former CIA director.

"General David Petraeus will stand in the ranks of America's greatest military heroes. His inspirational leadership and his genius were directly responsible – after years of failure – for the success of the surge in Iraq," McCain said.

Petraeus belonged to a new generation of officers who liked to describe themselves as scholar-warriors, having spent part of his career in academe. He was different from other such officers, though, in one important way – he was also extremely political, good at courting people in various administrations and in Congress.

He left West Point in 1974 and followed a conventional army career. It was his time in academia that made him different and helped him to the top of the military. While taking time out, he wrote extensively about the US experience in Vietnam, developing an alternative counter-intelligence philosophy.

He caught the attention of senior figures during his command of northern Iraq in the early days of the 2003 and George W Bush sent him back in 2007, with overall command of US and other international forces during the so-called surge. He then implemented the "hearts and minds" policy that he had developed during his Vietnam study, winning over Sunni tribal leaders to engage in operations against al-Qaida elements in what became known as the Sunni Awakening.

Petraeus returned to the US in 2008, to take over Central Command. When the senior commander in Afghanistan, General Stanley McChrystal, was forced to resign over comments reported in an article in Rolling Stone, Petraeus was called for again, this time by Obama.