The release of the heavily redacted 129-page report over the pardon of trader Marc Rich - an investigation that closed in 2005 without charges - triggered questions from Democrats already angered by the FBI's probe into hundreds of thousands of newly uncovered emails possibly linked to Hillary Clinton.
While the Rich documents were published online Monday, they received little notice until they were posted on Tuesday on a Twitter account for the Federal Bureau of Investigation's division managing Freedom of Information Act (FOIA) requests that had had no posts since a year ago, except for a small handful released simultaneously on Sunday.
"Absent a FOIA litigation deadline, this is odd," asked Hillary Clinton spokesman Brian Fallon.
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"Will FBI be posting docs on Trump's housing discrimination in '70s?" he added, referring to Clinton's Republican rival Donald Trump, a billionaire real estate magnate.
The FBI said the documents were posted shortly after they were processed, as with FOIA materials requested three or more times.
"Per the standard procedure for FOIA, these materials became available for release and were posted automatically and electronically to the FBI's public reading room in accordance with the law and established procedures," the statement said.
The FBI indicated that this was only a "preliminary" release that could therefore be followed by more.
Rich was indicted on federal charges of tax evasion in the United States. He was a fugitive from the Department of Justice - at a time one of the FBI's most wanted - living in exile in Switzerland at the time of his indictment. He died there in 2013.
In a controversial move, Bill Clinton pardoned him on his last day in office on January 20, 2001. The FBI opened its investigation into the pardon later that year.
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Rich's ex-wife Denise Eisenberg Rich, whose name was redacted from the FBI files, "has been a major political donor to the Democratic Party, and these donations may have been intended to influence the fugitive's pardon," reads a bureau note requesting that a preliminary investigation be opened.
Some of the donations went to the William J. Clinton Presidential Foundation, the predecessor to the Clinton Foundation, according to the document.
"It appears that the required pardon standards and procedures were not followed," reads the FBI document dated February 15, 2001.
The Rich case fell under the watch of current FBI Director James Comey, then a younger prosecutor.
The FBI document dump comes as Comey is under fire, from both Democrats and some Republicans, for effectively reopening in recent days the bureau's investigation into Hillary Clinton's use of a private email server.
In pitch to men, Obama says Clinton treated differently
US President Barack Obama hit the campaign stump for Hillary Clinton on Tuesday, telling voters not to be "bamboozled" by Donald Trump and making a specific pitch to wavering male voters.
Visiting the swing state of Ohio for the second time in a month, Obama challenged male voters to consider whether they were being sexist in hesitating between Trump and Clinton.
Obama's anointed Democratic successor is the favorite to win the election, but Trump appears to have closed in with just a week to go until polling day.
"I want every man out there to kinda look inside yourself," he said. "If you are having problems with this stuff, how much of it is that we're just not used to it?"
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"There is a reason we haven't had a woman president before," Obama told a raucous crowd on Columbus, Ohio - a state he won in 2008 and 2012.
"I want you to think about it because she's so much better qualified than the other guy."
It was during the 2008 campaign that Obama blocked Clinton's path to the presidency by winning the party primary.
Obama will barnstorm swing states almost every day this week, visiting North Carolina on Wednesday and Florida on Thursday before going back to North Carolina.
The popular outgoing president has been deployed to firm up tepid support for Clinton among key demographic groups that sent him to the White House.
