Former FBI director James Comey broke with protocol in his handling of the Hillary Clinton email investigation but his decisions were not driven by political bias, a watchdog has reportedly found.
The report from the inspector general also criticises Mr Comey for not keeping his superiors at the Justice Department, including then-attorney general Loretta Lynch, properly informed about his handling of the investigation, AP sources said.
The report’s findings are to be made public later on Thursday in the culmination of an 18-month review into one of the most controversial FBI investigations in recent history.
The report has long been expected to criticise the FBI’s handling of the Clinton email probe, stepping into a political minefield while examining how a non-partisan law enforcement agency became entangled in the 2016 presidential race.
President Donald Trump is looking to the report to provide a fresh line of attack against Mr Comey and his deputy, Andrew McCabe, as he claims that a politically tainted bureau tried to undermine his campaign and, through the later Russia investigation, his presidency.
Mr Trump is certain to try to use the report to validate his firing of Mr Comey last year.
But the report could do more to back Democratic claims that the FBI actually contributed to Mr Trump’s victory, most notably by reopening in the final days of the race its investigation into whether Mrs Clinton mishandled classified information.
That development unfolded as Mr Trump’s own campaign — unbeknownst at the time to the American public — also came under FBI investigation for possible coordination with Russia.
Inspector General Michael Horowitz, a former federal prosecutor appointed by President Barack Obama, prepared the report. Supporters from both parties regard him as apolitical.
His most significant report before this was the 2012 study of the botched Obama-era gun operation known as Fast and Furious.
The Clinton report will examine key actions by FBI leaders, including Mr Comey’s decision to publicly announce in July 2016 his recommendation against criminal charges for Mrs Clinton, and his disclosure to Congress days before the election that the investigation was being revived because of newly discovered emails.
An earlier inspector general report criticised Mr McCabe and led to his firing on allegations that he misled internal investigators about his role in a news media disclosure. He denies those charges.