Those emails, sent in late 2011 and early 2012, involve a discussion by the then-U.S. ambassador to Pakistan about a planned U.S.-led drone strike in that country, and took place largely on what's called "low side," or non-classified, State Department email system. The planned drone strike was later canceled.  The Wall Street Journal was first to report the details of planned drone strike email discussion.  The exchange in question took place over the December holidays when multiple officials were away from the office and without access to their classified email, and some of the emails were ultimately sent to Secretary Clinton's private email server, according to the official.  The FBI has not yet interviewed Clinton as part of its investigation. As CNN first reported, investigators have not found evidence to support criminal charges against Clinton and none are expected, but no final determination will be made until that interview has taken place.  The CIA drone program is covert and considered classified, so while it is widely discussed in public and in media reports, any discussion of the program on a non-classified system is a violation of government rules. For this reason, the CIA insisted that the emails on the subject be retroactively classified.  Discussion of classified matters on government non-classified email systems is a perennial problem that occurs widely in the government, but damage is typically contained because violators use government email systems. What is not common is a cabinet-level official using a personal server to conduct all official business, outside the protection of government email servers.  Some of Clinton's closest aides, including her  , have provided interviews to federal investigators, U.S. officials briefed on the investigation previously told CNN.  Clinton's campaign and State did not immediately respond for comment for this report. Clinton campaign officials have said she is cooperating fully with the Justice Department review.
A series of emails about the CIA's drone program are among those being investigated by the FBI as part of its probe into Hillary Clinton's use of a private email server while secretary of state, a law enforcement official tells CNN.