FBI Director James Comey. Thomson Reuters FBI Director James Comey told Congress on Sunday that the agency had completed its review of emails found on former Rep. Anthony Weiner's laptop that may have been relevant to the bureau's investigation into Hillary Clinton's private email server.

The new emails were uncovered after investigators seized devices they suspected Weiner, the estranged husband of top Clinton aide Huma Abedin, used to exchange sexually explicit messages with underage girls.

The reported 650,000 emails were reviewed over eight days and yielded no new evidence that compelled the FBI to change its initial decision made in July not to recommend charges against Clinton.

Many of the emails examined were apparently duplicates of those FBI agents reviewed when they investigated her private server between August 2015 and July 2016, since the emails were either sent or received with Clinton's private email address.

Comey wrote on Sunday that he and his team had been "working around the clock" to process the newly discovered emails, and that they "reviewed all communications that were to or from Hillary Clinton while she served as secretary of state."

Donald Trump. AP

Still, Republican nominee Donald Trump and his supporters were quick to raise questions about how the FBI could have examined so many emails in what seemed like so little time.

"IMPOSSIBLE: There R 691,200 seconds in 8 days," one of Trump's advisers, retired Lt. Gen. Michael Flynn, tweeted on Sunday afternoon. "DIR Comey has thoroughly reviewed 650,000 emails in 8 days? An email / second? IMPOSSIBLE."

Trump echoed Flynn's comments during a rally in Michigan.

"You can't review 650,000 new emails in eight days!" Trump said.

Defense Intelligence Agency Director US Army Lt. Gen. Michael Flynn testifies before a House committee in 2014. REUTERS/Gary Cameron

Cybersecurity experts, however, disagree.

"I see no problem with the FBI completing a search of this size in a week," John Michener, chief scientist at the cybersecurity firm Casaba Security, told Business Insider on Monday.

He added: "The vast majority of the emails are likely to be duplicates of emails that the FBI has already seen and evaluated. Those can be trivially eliminated. After that I would expect a keyword search to loop for things of interest."

On Twitter, former National Security Agency contractor-turned-leaker Edward Snowden said the process could be achieved by "old laptops" in hours or even minutes.

"Drop non-responsive To:/CC:/BCC:, hash both sets, then subtract those that match," Snowden said, responding to a question posed by Jeff Jarvis, a professor at the City University of New York Journalism School, about how long it would take the NSA "to dedupe 650k emails."

A former FBI agent corroborated those assessments in an interview with Wired, saying "you can triage a dataset like this in a much shorter amount of time."

"We'd routinely collect terabytes of data in a search," said the unnamed agent. "I'd know what was important before I left the guy's house."

The FBI has not revealed the process by which it sifted through all of the relevant emails, but most experts agree that the agents probably didn't even need the full eight days to do so.

"Given those emails, and a list of known email accounts from Hillary and associates, and a list of other search terms, it would take me only a few hours to reduce the workload from 650,000 emails to only a couple hundred, which a single person can read in less than a day," cybersecurity consultant Rob Graham wrote in a blog post on Sunday.

Michener largely agreed.

"This is a well-developed area for both the FBI and the legal industry in general," Michener told Business Insider. "It's not a complicated or improvised process. I'm sure the FBI already had all of its search terms set up in a database, so all they had to do was run them against the new data set. This is just a minor delta, and totally reasonable for them to complete it in that span of time."