July 10, 2015: The FBI’s Clinton investigation formally begins.

In September 2016, the FBI will reveal in a publicly released report, “On July 10, 2015, the Federal Bureau of Investigation (FBI) initiated a full investigation based upon a referral received from the US Intelligence Community Inspector General (ICIG), submitted in accordance with Section 81 1(c) of the Intelligence Authorization Act of 1995 and dated July 6, 2015, regarding the potential unauthorized transmission and storage of classified information on the personal email server of former Secretary of State Hillary Clinton. The FBI’s investigation focused on determining whether classified information was transmitted or stored on unclassified systems in violation of federal criminal statutes and whether classified information was compromised by unauthorized individuals, to include foreign governments or intelligence services, via cyber intrusion or other means.” (Federal Bureau of Investigation, 9/2/2016)

However, according to an account by CNN in August 2015, the FBI had already begun investigating Clinton’s emails in late May 2015, so presumably this merely formalized it. (CNN, 8/20/2015)