Long-Time Clinton Aide Cheryl Mills Was Granted Limited Immunity In Now-Closed Email Investigation FBI Documents Show Aide Cheryl Mills Was Granted Limited Immunity In Exchange For A Laptop Search During Now-Closed Clinton Email Investigation. On September 23, Rep. Jason Chaffetz (R-UT) told The Associated Press (AP) he was “absolutely stunned” that long-time Hillary Clinton aide Cheryl Mills had been granted an immunity deal in the course of the now-closed FBI investigation into Clinton’s use of a private email server while secretary of state.