The FBI stumbled upon a trove of emails from one of Hillary Clinton's top aides weeks ago, law enforcement officials told CNN Sunday.
But FBI Director James Comey didn't disclose the discovery until Friday, raising questions about why the information was kept under wraps and then released only days before the election.
Meanwhile, the Justice Department has obtained a warrant that will allow it to begin searching the computer that is believed to contain thousands of newly found emails of top Clinton aide Huma Abedin, two law enforcement sources confirmed to CNN.
The timeline behind the discovery of the emails came into greater clarity Sunday.
Investigators took possession of multiple computers related to the inquiry of Anthony Weiner in early October, U.S. law enforcement officials said. Weiner is Abedin's estranged husband and is being probed about alleged sexting with a purportedly underage girl.
Technical experts at the FBI began procedures to catalogue the emails found on one of the computers and soon found emails belonging to Abedin. The discovery surprised investigators, triggering legal issues because the search warrant was limited to the sexting case. That's why the Justice Department sought the new search warrant.
Senior officials at the FBI, including Andrew McCabe, the FBI deputy director, were briefed on the issue. By mid-October, Comey learned investigators in the Weiner case might have found something that could have an impact on the now-closed probe into Hillary Clinton's private email server, according to one law enforcement official.
Comey was told investigators were still trying to figure out how many emails existed and their pertinence to the Clinton probe.
Senior Justice Department officials were briefed on the situation about a week ago and Comey was given a full briefing Thursday, the officials said, triggering his decision to notify members of Congress Friday that the FBI was reviewing emails potentially related to Clinton's server.
The news regarding the timing of the computer's seizure was first reported Sunday by The Washington Post.
Comey's notification to Congress of the review is rocking the final days of the presidential race. Democrats are furious that Comey would revive the explosive issue of Clinton's email server so close to the election. Donald Trump, meanwhile, is seizing on the review after spending weeks on the defense, hoping it will be a potent issue he can ride until the end of the contest.
Clinton campaign chairman John Podesta blasted Comey on Sunday for disclosing the review.
"He might have taken the first step of actually having looked at them before he did this in the middle of a presidential campaign, so close to the voting," Podesta said on CNN's "State of the Union."
Abedin hasn't spoken publicly about the newly found emails.
"The possibility that this device contains any emails of hers is news to her," a source familiar with the investigation and civil litigation told CNN. "The device supposedly at issue now belonged to Anthony, not her."
The computer in question is considered to belong to Weiner.
Prior to obtaining the warrant, investigators saw enough of the emails to determine that they appeared pertinent to the previously completed investigation and that they may be emails not previously reviewed.
Agents saw enough of the emails that they believed there could be classified information and that it warranted further inquiry, law enforcement sources told CNN.
Because they didn't have a warrant specific to Abedin's emails, officials weren't able to further examine them. Justice Department and FBI officials view Abedin as cooperative with the investigation.
FBI officials don't yet know how many of the emails are duplicates of emails they already have reviewed as part of the Clinton email server investigation and whether any of them may contain classified information.
Investigators believe it's likely the newly recovered trove will include emails that were deleted from the Clinton server before the FBI took possession of it as part of that earlier investigation.
FBI officials expect they have to interview Abedin again after they have gone through the emails.