The FBI has assigned its elite "A-Team" to lead what is now being described as a "extremely serious" investigation into former Secretary of State Hillary Clinton's use of a private email system during her tenure at the State Department.

Investigators are looking into whether Clinton violated a section of the Espionage Act, 18 US Code 793, which pertains to "gathering, transmitting or losing defense information," reported Fox News.

The FBI launched a criminal probe earlier this month into Clinton's use of a private server, which was not equipped to handle classified information. After the intelligence community's inspector general determined that two emails found on Clinton's server contained information classified as "top secret" at the time they were sent, Clinton finally turned over the private home-brew server to the bureau after refusing to do so for months.

Clinton initially claimed, on multiple occasions, that she never sent or received classified information, but she soon walked back on those claims, instead saying she never sent information that was marked as being classified.

A number of federal guidelines exist warning officials that certain information is automatically deemed classified when generated, but it appears as though Clinton either ignored or was ignorant of these warnings and allowed dozens of emails containing information automatically deemed classified to pass through her server, as HNGN previously reported.

That being the case, the FBI is also looking into whether Clinton should have known "based on the quality and detail of the material that emails passing through her server contained classified information regardless of the markings," Fox News reported.

Judge Andrew Napolitano previously told Fox News that Clinton could be charged with a felony for each email she sent that contained classified information.

As for the Espionage Act provision currently in question, a leading national security attorney told Fox News that violating it is also a felony.

"Under [sub-section] F, the documents relate to the national defense, meaning very closely held information," attorney Edward MacMahon Jr. said. "Somebody in the government, with a clearance and need to know, then delivered the information to someone not entitled to receive it, or otherwise moved it from where it was supposed to be lawfully held."