 Live from NPR News in Washington, I'm Dave Mattockley. The FBI says the gunman it believes carried out Saturday's attempted assassination of former President Donald Trump at a rally in Pennsylvania acted alone. 20-year-old Thomas Matthew Crooks was shot and killed by the Secret Service on the rooftop of a building in the city of Butler moments after Trump was wounded in his right ear as he spoke on stage. Three attendees were also shot, one fatally.