The Washington Post via Getty Images
- A shooter armed with an AR-15 rifle opened fire on Donald Trump during a rally in Pennsylvania.
- The FBI said it is working "tirelessly" to identify a motive behind the attempted assassination.
- Acquaintances of the man who conducted the shooting said they were in shock.
As details emerge about the background of the man who tried to assassinate Donald Trump, his motive remains a mystery.
The shooter, who has been named Thomas Matthew Crooks, 20, of Bethel Park, Pennsylvania, tried to kill Trump during a rally in Pennsylvania.