Updated at 7:30 p.m. ET
Federal agents now have a search warrant they need to examine the thousands of emails found on a computer belonging to former U.S. Rep. Anthony Weiner that could be pertinent to the investigation of Hillary Clinton's personal email server, sources familiar with the matter tell NPR's Carrie Johnson.
Weiner is the estranged husband of Clinton aide Huma Abedin.
On Friday, FBI Director James Comey disclosed to lawmakers the emails had been found during an investigation into Weiner, who is under scrutiny for allegedly sending illicit text messages to a minor.
Sources tell NPR that the emails appear to come from a laptop that Weiner and Abedin sometimes shared. The investigators' theory is that Abedin apparently used the laptop at home for some correspondence that could be related to State Department business, sources said.
It is not clear whether any of the newly discovered emails were sent or received by Clinton.
Another key question is whether the documents are copies of material already reviewed by the FBI during its yearlong investigation into Clinton's email server, or whether they are new — and whether they contain classified material.
Top officials at the Justice Department and FBI have issued orders to review the emails as quickly as possible, a source said. If they are duplicates, that work could go rapidly; if not, it could take more time.
The material was first discovered in early October, and it's not clear why no warrant was sought then. A source also said that the material would have to contain something extraordinary to change the original determination not to bring any charges against Clinton or her associates.
Here's what else we've learned — or are still asking about — since Friday's announcement.
Things We Know
How were these emails discovered?
The new emails were discovered through a criminal investigation of former New York Rep. Anthony Weiner, the estranged husband of top Clinton aide Huma Abedin. Weiner allegedly sent illicit text messages to an underage girl. The FBI was examining devices including a laptop, a phone and an iPad that Weiner and Abedin sometimes shared. The emails in question emanated from the laptop.
Why did Comey alert Congress?
When Comey sent the letter to congressional committee chairs on Friday, he also sent a message to his employees that sheds light on his decision. In that letter, which was obtained by the Washington Post, Comey wrote:
"We don't ordinarily tell Congress about ongoing investigations, but here I feel I also think it would be misleading to the American people were we not to supplement the record. At the same time, however, given that we don't know the significance of this newly discovered collection of emails, I don't want to create a misleading impression. In trying to strike that balance, in a brief letter and in the middle of an election season, there is significant risk of being misunderstood, but I wanted you to hear directly from me about it."
Why is Comey facing criticism for his decision?
Some lawmakers and law enforcement officials have criticized Comey for bringing this new information to light just days before the election.
Former federal prosecutor Peter Zeidenberg, who worked at the Justice Department for 17 years, told NPR's Rachel Martin, "The information that they provided just invites speculation without informing the public about what's going on."
"It's pretty extraordinary to make an announcement like this 11 days before the election. ... We don't know what's in these emails. We don't know if they're relevant," Zeidenberg said.
Zeidenberg, who is supporting Clinton in this election, said it would have made more sense for Comey to review the emails first to see if any information in them was relevant to the investigation, and then make an announcement — even if it happened after Election Day.
Former Attorney General Alberto Gonzales told NPR's Michel Martin he was "mystified" with the development. Gonzales said the Justice Department typically has the last word as to whether or not to move forward with prosecution. In this case, NPR has confirmed that Comey went against Attorney General Loretta Lynch's recommendation by releasing the new information.
"It is fair to say that we do have protocols in place, and it appears that many of those protocols have not been followed here," Gonzales said. "We have a very unique situation, a very volatile election, two very high-profile candidates. You want to be very careful about what you do."
Gonzales said he was hesitant to question Comey without knowing all the facts. But, he added, "The FBI director has been out on his own, quite frankly, with respect to this investigation."
A former senior official at the Department of Justice, who requested that he remain anonymous, told NPR that Comey has been mishandling the Clinton investigation since the July press conference when he announced the FBI's findings.
"You don't hold press conferences to announce that someone should not be charged with a crime and then proceed to dump all over that person and to publicly discuss the evidence against them," he told NPR. "You don't publicly announce that you're conducting a criminal investigation against someone. And you especially don't do it if that person is a candidate, 11 days before an election. That's true whether it's a presidential election or an election for dog catcher."
Former Justice Department official Carrie Cordero said Comey's disclosure was necessary after Lynch's meeting with Bill Clinton on an airplane this summer fueled distrust of the impartiality of the Justice Department and the FBI.
How are members of Congress reacting?
Senate Democratic leader Harry Reid blasted Comey in a letter on Sunday, suggesting he may have broken the law with his announcement (more on that debate below) and calling his character into question.
"I led the fight to get you confirmed because I believed you to be a principled public servant," Reid wrote. "With the deepest regret, I now see that I was wrong."
Comey has spoken to members of Congress about the review of the new emails. Republican Rep. Bob Goodlatte, chairman of the House Judiciary Committee, told ABC that he and Rep. John Conyers, the committee's ranking Democrat, spoke with Comey on Friday. They encouraged the FBI director to release more information as soon as possible, but said Comey didn't commit to release more information. He added that Comey is "very conscious" of dissent within the FBI over the decision not to prosecute Clinton.
Rep. Adam Schiff, a Democrat from California, told ABC, "That kind of an ambiguity bomb, this close to election, was a terrible lapse in judgment."
House Speaker Paul Ryan responded to the development in a statement, saying, "Yet again, Hillary Clinton has nobody but herself to blame." He called her private email server "reckless" and urged the director of National Intelligence to suspend classified briefings with Clinton "until this matter is fully resolved."
What are the candidates saying?
Clinton has urged the FBI to release more information and explain the facts.
"It's pretty strange to put something like that out with such little information right before an election," Clinton said at a Florida rally on Saturday. "It's not just strange. It's unprecedented, and it is deeply troubling."
Clinton, who said her campaign found out through the media, also said that Comey "doesn't know whether the emails referenced in his letter are significant or not."
Clinton Campaign Chairman John Podesta told CNN's Jake Tapper, "If they're not significant, they're not significant. So 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."
Donald Trump has been using the new developments to emphasize his stance that Clinton is corrupt.
"The investigation is the biggest political scandal since Watergate, and it's everybody's hope that justice at last can be delivered," Trump said this weekend at a rally, as the crowd broke out in chants of "lock her up."
Things We Don't Know
What's in the emails?
We don't know — and it seems like nobody else does either.
The news that the FBI obtained a warrant to search the emails in question is a step toward finding out. A key question is whether the emails are duplicates of those already submitted in the course of the Clinton email investigation. If they are not, the review will take longer.
When will this be resolved?
There is no timeline set for the investigation. As NPR's Carrie Johnson reported, this new phase of the investigation could continue for a long time, well past the inauguration of the next president.
If the emails are all duplicates of previously reviewed material, that may be known this week.
Two law enforcement sources also told Johnson that the Department of Justice has no foreseeable plans to talk publicly about the Clinton emails. But that is not satisfying some Democrats. A letter from Sens. Dianne Feinstein, D-Calif., Tom Carper, D-Del., Patrick Leahy, D-Vt., and Ben Cardin, D-Md., asks for "more detailed information about the investigative steps that are being taken, the number of emails involved, and what is being done to determine how many of the emails are duplicative of those already reviewed by the FBI" by Monday.
Were the FBI's actions proper?
A couple of legal questions have been raised about the conduct of the FBI and its director.
In addition to the FBI obtaining a warrant to search the emails, a broader question of whether the FBI had the authority to look into emails related to the Clinton investigation while investigating Anthony Weiner has been raised.
And a complaint from Richard Painter, a former White House ethics lawyer in the Bush administration, has been filed against Comey alleging he violated the 1993 Hatch Act, which bars government officials from using their positions to influence elections. Senate Minority Leader Harry Reid made the same suggestion in a letter to Comey on Sunday.
Just like questions about the substance of this email discovery, the answers are not clear here, either.
Comey already told Congress that neither Clinton nor her aides lied to FBI agents when they were interviewed. In the earlier investigation, Comey found no efforts by Clinton or her aides to obstruct justice or betray the United States. Unless something substantial emerges from this new set of emails, it's unlikely a criminal prosecution will occur.
As former Attorney General Alberto Gonzales told NPR, "Sometimes you may make an announcement about an investigation and then you turn out not to do anything about it, but nonetheless it adversely affects someone's life."
Will this influence the outcome of the presidential race?
A spate of new polls gauging the state of the race nationally and in key battleground states emerged Sunday. While a lot of those polls show the race tightening, they were largely taken before this news broke on Friday. That reflects Republicans coming back to Trump after distancing themselves after the release of the 2005 Access Hollywood video and accusations of sexual assault.
So we'll have to wait a few more days to see if the race is really shifting in the aftermath of this bombshell. But at this point in a campaign, there are many factors affecting shifts in polling.
In a previous version of this story, former Attorney General Alberto Gonzales' name was misspelled as Gonzalez.