Story highlights The probe is considered over with regard to Clinton

Technology was key to the effort

Washington (CNN) In the days since the FBI dropped a bombshell into the presidential race with the discovery of new emails relevant to the Hillary Clinton server investigation, bureau investigators worked "around the clock" to review the large volume of emails, two law enforcement officials told CNN.

Key to the effort was software that was refined from its previous uses for the review of emails found on a device belonging to Anthony Weiner, the disgraced former congressman and estranged husband of Clinton's top aide, Huma Abedin.

"A lot of this was a matter of technology," one official said. "Without the technology, this would have taken a lot longer."

The news that the FBI was confident in its July conclusion that there was not enough evidence to support criminal charges related to the server came in a letter from Comey to Congress on Sunday. That was the same way that Comey had initially thrown the presidential race into flux late last month, when he sent a letter to Congress saying newly discovered emails on Weiner's device, which came up in a separate investigation, were being looked at in relation to the Clinton investigation.

Now, the probe is considered over with regard to Clinton.

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