What to Know About the New Clinton-Related Emails

— -- The revelation that the FBI is working to review a cache of newly discovered emails potentially tied to the agency’s probe of Hillary Clinton’s private email server has jolted her campaign and put FBI Director James Comey in the crosshairs of even longtime supporters. But exactly what do we know about the emails? The bottom line: not much.

It’s still too early to say whether any of the newly discovered emails are truly new to FBI agents who have been investigating the matter for more than a year. And it’s still too early to say whether any of the emails contain any type of sensitive information.

As one source close to the matter put it on Saturday, “We don’t know what this is yet.”

Here’s what we do know:

Why These Emails Could Matter – or Not at All

The FBI came to its conclusion that Clinton committed no crimes in her use of a private server after reviewing tens of thousands of emails that passed through the server, including thousands of emails recovered by the FBI after Clinton’s lawyers deemed them not work related and deleted them.

The new cache of emails — on a laptop used by Clinton aide Huma Abedin — could provide the FBI with messages that investigators were unable to recover. After all, Abedin and two other top aides accounted for more than two-thirds of emails sent directly to Clinton on the private server, according to the FBI.

Comey wrote in a letter to lawmakers that the newly discovered emails “appear to be pertinent to our investigation,” but the FBI previously found no evidence to suggest Clinton or her aides knowingly sent or received classified information on the private server or to indicate that sensitive emails were accessed by foreign hackers.

But Comey said in a message to FBI colleagues on Friday, “We don’t know the significance of” the emails. “There is significant risk of being misunderstood.”

The emails may not offer anything new to the FBI. And even if new messages are found, they may not change any of the FBI’s conclusions in the case. Or they may.

How These Emails Were Found

These emails were found by chance. Earlier this year FBI agents in New York were analyzing a laptop used by former Rep. Anthony Weiner of New York, who was accused of sending sexually explicit messages to an underage girl. During that review, agents came across some emails sent or received by Abedin, Weiner’s now estranged wife. She is one of Clinton’s most trusted aides, and she was among only a handful of people who had an email address from Clinton’s private server.

What Happened at the FBI Afterward

The discovery of emails potentially relevant to the Clinton-related probe — by investigators not involved in the probe — sparked a complicated process at the FBI, according to sources. For weeks, agents separately working on the Clinton and Weiner investigations and their superiors engaged in a back-and-forth over how to handle the situation. A key question for them was whether the FBI needed to obtain a warrant in order to review the emails, since they were discovered in the course of a separate and unrelated investigation.

The investigators working on the Clinton email probe put together a summary of the situation, and on Thursday they presented it to Comey, who agreed with their assessment that a warrant was needed. Because Comey previously told Congress — and the public — that the Clinton probe was “closed,” he sent lawmakers a letter the next day, informing them of further “investigative steps” in the matter. On Sunday the FBI obtained the appropriate warrant and began reviewing thousands of emails.

Huma Abedin Used At Least Three Private Email Accounts

It’s unclear exactly how the emails now being reviewed by the FBI ended up on a personal device used by Abedin and Weiner. During her interview with FBI agents in April, Abedin said she had used three non-government email accounts: the account associated with Clinton’s private server, a Yahoo account, and an account tied to Wiener’s political campaign.

The emails being reviewed could be from one or more of those accounts.

According to a summary of Abedin's interview released by the FBI, she would use the Yahoo account and the private-server account “if her [government] account was down or if she needed to print an email or document.”

Abedin “routinely forwarded emails from her state.gov account to either her clintonemail.com or her yahoo.com account so that she could print them,” the summary said. “ABEDIN [sic] stated that she would typically print the documents without reading them.”

Abedin also said she didn’t look at the emails when printing them and didn’t make judgments over whether they contained classified information, according to the FBI.

“[S]he relied on the sender to make that assessment and to properly mark and transmit the document,” according to the interview summary.

The FBI Is Under Fire From All Sides

Sources say top FBI officials have been taken aback by the breadth of criticism coming their way since Friday’s revelation, with growing questions over the timing of the announcement and the bare-bones nature of the disclosure.

On Saturday widely circulated media accounts cited concerns from senior Justice Department officials who believed Comey’s disclosure to Congress violated long-standing department tradition to steer clear of potentially influential investigative actions close to an election.

The Clinton campaign and Democratic allies were particularly upset by Comey’s move, with Senate Minority Leader Harry Reid accusing the FBI chief of trying to influence the election and saying he now regrets supporting Comey to lead the agency.

“[You are] tarring Secretary Clinton with thin innuendo,” Reid said. “You rushed to take this step 11 days before a presidential election, despite the fact that for all you know, the information you [now] possess could be entirely duplicative of the information you already examined which exonerated Secretary Clinton.”

Even some of Donald Trump’s most vocal supporters called foul.

Former Rep. Joe Walsh, a controversial Republican who recently vowed to grab his musket if Clinton wins the presidency, tweeted, “I want Trump to win, but what Comey just did to Hillary Is wrong & really unfair to her” and “Hillary is corrupt as hell, but the FBI Dir has no right to mess with an election.”

On Sunday nearly 100 former federal prosecutors from both sides of the aisle, including former Attorney General Eric Holder, released a letter saying they are “both astonished and perplexed” by Comey’s “unprecedented decision to publicly comment” about the newly discovered emails.

“Often, evidence uncovered during the course of an investigative inquiry is incomplete, misleading or even incorrect, and releasing such information before all of the facts are known … can unfairly prejudice individuals and undermine the public’s faith in the integrity of our legal process,” the letter said.

Comey’s notification to Congress “acknowledges the information to be examined may not be significant or new,” but his “disclosure has invited considerable, uninformed public speculation,” according to the letter.

ABC News’ Pierre Thomas, Geneva Sands, Jack Date, Lucien Bruggeman and Ali Rogin contributed to this report.