An “extremely serious” investigation has begun into allegations that Democratic presidential nominee hopeful Hillary Clinton used a private email server during her term as secretary of state — and the FBI’s “A-team” has been put on the case, according to reports.

A source told Fox News that an investigation is earnestly pursuing Hillary Clinton based on 18 US Code 793, which is a section in the Espionage Act that has to do with gathering and transmitting national defense information, according to a Reuters report.

It centers around two emails that were found on Clinton’s server between 2009 and 2011 that contained information that is considered “top secret/sensitive compartmented information, which is one of the highest possible levels of classifications. They were from a bath of 40 randomly selected from about 30,000 emails that were considered work-related that Clinton turned over to the State Department from her time as secretary of state between 2009 and 2013.

It is a crime to not only knowingly mishandle what are considered state secrets, but to use them in a manner that could compromise the safety of the United States, and therefore the FBI investigation with its “A-team” will go beyond what an Inspector General for the intelligence community would normally do, according to the report, which quotes from Time’s source.

And it’s an unusual case for another reason: most cases are run out of the 56 field offices of the FBI, but this one will be run from its headquarters in Washington, D.C. This is because of how important this inquiry is, and the need in the FBI’s eyes to keep the investigation as close to the nation’s capital by running it in the coutnerintelligence section of the FBI.