Intelligence Community Inspector General Charles McCullough and State Department Inspector General Steve Linick jointly send the FBI a “security referral,” asking the FBI to investigate Clinton’s private emails and server. This grew out of McCullough and Steve Linick reviewing some of the over 30,000 Clinton emails handed over to the State Department in December 2014. (The Los Angeles Times, 3/27/2016) (The Washington Post, 8/14/2015)
However, according to another account by CNN in August 2015, the FBI had already begun investigating Clinton’s emails in late May 2015, so presumably this referral would only have spurred on that effort. (CNN, 8/20/2015) The FBI formally begins their Clinton investigation four days later, on July 10, 2015.