Thomas Matthew Crooks attempted to assassinate Donald Trump during a campaign rally in Butler, Pennsylvania, firing eight shots from an AR-15-style rifle.Crooks was killed by a Secret Service agent after the attack, which left firefighter Corey Comperatore dead and two others seriously injured.Investigations revealed Crooks' radical shift from "rabidly pro-Trump" to "rabidly anti-Trump" online, with allegations of an FBI cover-up about his activity and political ties.