The FBI revealed Friday it was reviewing a new batch of emails that "appear to be pertinent" to its previous investigation into Hillary Clinton's use of a private server — and multiple federal officials told NBC News they were found as part of an on-going probe of disgraced former New York congressman Anthony Weiner.
The emails were found on a laptop that Weiner allegedly used to send inappropriate text messages and pictures to an underage girl, the sources told NBC News.
Investigators also discovered Weiner's wife, Huma Abedin, had used the same laptop to send emails to Clinton and now they are checking those messages to see if there was any classified information on them, the sources said.
Abedin, who is Clinton's closest aide, is separated from Weiner.
Clinton said the FBI has not been in touch with her and called on Director James Comey to release whatever emails they found immediately. She said she has no idea what they might be but added, "I'm confident whatever they are will not change the conclusion reached in July."
The Democratic nominee was referring to the FBI investigation of her use of a private email server while secretary of state which ended with no criminal charges against her.
"Voting is already underway, so the American people deserve to get the full facts immediately," she said during a brief press conference.
Asked if it will affect the election, which most polls show her winning, Clinton said, "I think people made up their minds a long time ago."
In his letter to the Senate Judiciary Committee announcing the discovery of the emails, Comey made no mention of Weiner, who resigned in disgrace in a sexting scandal.
"In connection with an unrelated case, the FBI has learned of the existence of emails that appear to be pertinent to the investigation," Comey wrote. "I agreed that the FBI should take appropriate investigative steps designed to allow investigators to review these emails to determine whether they contain classified information, as well as to assess their importance to our investigation."
A senior law enforcement official told NBC News Friday that the Comey letter was sent to the Hill "out of an abundance of caution" and to be extra-thorough.
There's no indication, the official said, that Clinton, her campaign or the State Department withheld information about the contents on Weiner's laptop.
The politically explosive revelation came just 11 days before Election Day and a top Clinton aide told NBC News that neither the candidate nor the campaign got any advance warning that Comey's letter was coming.
"It boggles the mind why this step was taken with just 11 days to go," Clinton campaign spokesman Brian Fallon said.
Comey should "provide the American public more information than is contained in the letter he sent to eight Republican committee chairmen," Clinton campaign chairman John Podesta said in a statement.
"Already, we have seen characterizations that the FBI is 'reopening' an investigation but Comey's words do not match that characterization," he said. "Director Comey's letter refers to emails that have come to light in an unrelated case, but we have no idea what those emails are and the Director himself notes they may not even be significant. It is extraordinary that we would see something like this just 11 days out from a presidential election."
Tim Kaine, Clinton's vice presidential running mate, who was at an early voting site in Tallahassee on Friday, told reporters "gotta read a little more, gotta read a little more" before continuing on.
Related: Read the Letter
Donald Trump called the revelation "bigger than Watergate" and praised the FBI for having "the courage to right the horrible mistake they made," an apparent reference to the agency's decision earlier this year to not press criminal charges against Clinton.
"I need to open with a very critical breaking news announcement," Trump said at a campaign rally in New Hampshire. "The FBI has just sent a letter to Congress informing them that they have discovered new emails pertaining to the former Secretary of State Hillary Clinton's investigation."
"This was a grave miscarriage of justice," he said, "it is about to be corrected."
The Republican-led House Judiciary Committee also applauded the FBI's move.
"The FBI's decision to reopen its investigation into Secretary Clinton reinforces what the House Judiciary Committee has been saying for months: the more we learn about Secretary Clinton's use of a private email server, the clearer it becomes that she and her associates committed wrongdoing and jeopardized national security," the Judiciary Committee said in a statement.
But Comey, who is also a Republican and who took a lot of heat in July for his agency's decision to not charge Clinton with a crime, did not say in the letter that he was reexamining the FBI's previous finding, which concluded that her handling of the emails was sloppy but not criminal.
Documents related to the case were released just before the Labor Day weekend and included a summary of Clinton's July interview with the FBI about her private email server, as well as a detailed investigative summary of the case.
It is unusual for the FBI to tell Congress, as Comey did, that it is looking over newly discovered evidence in a criminal inquiry that was otherwise closed.
Federal practice is not to comment on ongoing investigations, or discuss details of concluded investigations. Comey previously explained his departure from that practice in his earlier congressional testimony, given the special nature of this case and congressional oversight inquiries.
Still, some congressional Democrats told NBC News Friday that they are frustrated that Comey issued the letter reopening this issue without providing much in the way of specifics.