FBI agents interviewed Hillary Clinton for 3 1/2 hours today - a signal that the investigation into her use of a private email account while she was US Secretary of State is drawing to a close.

Clinton campaign spokesman Nick Merrill said that Clinton "gave a voluntary interview this morning about her email arrangements while she was Secretary," and added, "She is pleased to have had the opportunity to assist the Department of Justice in bringing this review to a conclusion".

Asked if the interview was businesslike and civil, Clinton told MSNBC that it was "both".

The investigation is not over: Agents and prosecutors will now have to compare what the presumptive Democratic presidential nominee said to other evidence they have gathered, including from interviews with Clinton's aides. They will also have to analyse how the facts of the case apply to various laws that might have been violated.

Advertisement

But officials familiar with the probe and legal analysts have said a meeting with Clinton would be reserved for the end of the investigation.

"That's certainly a signal that they're wrapping things up," said Justin Shur, a former deputy chief of the Justice Department's public integrity section who is now in private practice at the MoloLamken firm.

A Justice Department spokesman declined to comment, and Merrill said that Clinton would not comment further on her interview, which took place at FBI headquarters, "out of respect for the investigative process".

The past week has been tumultuous for Clinton and the Government's investigation into whether her email system might have compromised classified information. On Tuesday, former President Bill Clinton had an impromptu meeting with US Attorney-General Loretta Lynch on board Lynch's plane at an airport in Phoenix. Lynch asserted they did not discuss any pending investigations, but the conversation sparked an uproar - with some Republicans and Clinton rivals calling for a third party to be appointed to handle the case.

On Saturday, Lynch announced that she would accept recommendations from career prosecutors and FBI agents leading the probe - a decision that she said had been made before her meeting with Bill Clinton, but one that was surely meant to quiet criticism about the independence of the probe. While Lynch did not formally recuse herself from the investigation involving Hillary Clinton's email - saying that "would mean I wouldn't even be briefed on what the findings were" - she seemed to promise she would not veto whatever decision came from federal prosecutors handling the case.

It is not clear who precisely will be the ultimate decision-maker, if Lynch will serve as more of a rubber stamp. The Attorney-General said FBI Director James Comey would be among those involved.

The investigation is focused on whether classified information was mishandled because Clinton used a private email account when she was Secretary of State. The State Department's inspector general has already issued a report highly critical of Clinton's email practices, asserting that she failed to seek legal approval to use a private server and that staffers would not have assented if they were asked. The inspector general also found that Clinton's email setup was "not an appropriate method" for preserving public records.

A Washington Post analysis of Clinton's publicly released correspondence found that Clinton wrote 104 emails that she sent using her private server while Secretary of State that the Government has since said contained classified information.

But the review also found that using non-secure email systems to send sensitive information was widespread at the department and elsewhere in government and that Clinton's publicly released correspondence included classified emails written by about 300 other people inside and outside the government.

People familiar with the case have said previously that charges against Clinton seemed unlikely and that there was a particular void of evidence showing she intended to mishandle classified information, although they asserted investigators were still probing the matter aggressively.

The interview with Clinton was always seen as critical. If the former Secretary was untruthful with investigators, she could be charged with making false statements. That charge was contemplated in the case against retired Army general and former CIA Director David Petraeus, although he ultimately pleaded guilty to a misdemeanor charge of mishandling classified information.

With the Republican and Democratic conventions looming later this month, timing has also become a complicating factor. Justice Department guidelines specifically warn prosecutors against selecting the timing of investigative steps for the purpose of affecting an election or helping a particular candidate or party.