FBI agents knew of Hillary Clinton-related emails weeks before director was briefed

The FBI agents investigating Hillary Clinton's use of a private email server knew early this month that messages recovered in a separate probe might be germane to their case, but they waited weeks before briefing the FBI director, according to people familiar with the case.

FBI director James B. Comey has written that he was informed of the development on Thursday, and he sent a letter to legislators the next day letting them know that he thought the team should take "appropriate investigative steps designed to allow investigators to review these emails".

It is unclear why FBI agents delayed in telling James Comey about the emails. Picture / AP

That missive ignited a political firestorm less than two weeks before the election. Almost instantly, Comey came under intense criticism for his timing and for bucking the Justice Department's guidance not to tell Congress about the development.

It is unclear why - given the Clinton email team knew for weeks that they might have cause to resume their work - they did not tell Comey sooner. People familiar with the case said they had known about it since soon after New York FBI agents seized a computer related to their investigation into former congressman Anthony Weiner, who is alleged to have exchanged explicit messages with a 15-year-old girl. Weiner is the estranged husband of long-time Clinton aide Huma Abedin, and federal law enforcement officials said they believe the computer was used by both of them.

A public revelation in early October might have been less politically damaging for Clinton than one coming less than two weeks before the November 8 election. It is also unclear what agents have been doing in the intervening time - for instance, whether they were trying to learn more about the emails before notifying Comey. An FBI spokesman declined to immediately provide a statement.

A Washington Post-ABC News tracking poll found more than six in 10 likely voters said the FBI's announcement would make no difference in their vote. A little more than 3 in 10 said the news made them less likely to support Clinton, though about two-thirds of those were Republicans or Republican-leaning independents.

Comey wrote in his letter to Congress, "we don't know the significance of this newly discovered collection of emails", and federal law enforcement officials have said in recent days that investigators on the Clinton email team still had yet to thoroughly review them. They would need a warrant to do so, and Yahoo! News reported Saturday they had not yet acquired one.

Officials familiar with the case said the messages number in the thousands and include correspondence of Abedin and Clinton - though it was unclear if Clinton was the sender of any emails. Abedin has told people she is unsure how her emails could have ended up on a device she viewed as belonging to her husband, according to a person familiar with the investigation and civil litigation over the matter.

Comey in July announced he was recommending the probe into Clinton's use of a private email server while she was secretary of state be closed without charges - though he said investigators had found classified information on the server and characterised Clinton's and her aides' conduct as "extremely careless".

Provided they get the legal authority to do so, investigators will now be looking at whether the newly uncovered emails contain classified information or other evidence that could help advance the Clinton email probe. It is possible, though, that the messages could be duplicates of others already recovered elsewhere, or that they could be a collection of benign, personal notes.

Legislators on both sides of the political aisle are likely to raise questions about why the team investigating Clinton's private email took so long to brief Comey. Clinton and her backers have pushed aggressively for the bureau to release more information about its findings and criticised the agency for making its work public without knowing more. Republican presidential candidate Donald Trump has called the matter "the biggest scandal since Watergate" and suggested that the case against Clinton was now "so overwhelming".