Aaron Zebley served previously as Mueller's chief of staff at the FBI and as a senior counselor in the National Security Division at the Department of Justice. He also served as an assistant U.S. attorney in the National Security and Terrorism Unit in Alexandria, Virginia.

He is often referred to in the media as Mueller's "right-hand man."

Also, in 2015 when he was a lawyer, he represented Justin Cooper, the IT staffer who personally set up Hillary Clinton's unsecure server in her Chappaqua home, Fox News' Tucker Carlson revealed on his show Thursday.

Cooper, it so happens, is also the aide who destroyed Clinton's old BlackBerries with a hammer.