evidence: The FBI say Thomas Matthew Crooks, the man who shot at Trump at a Butler, Pa., political rally on Saturday, is believed to have acted alone. There is yet to be an established motive for Crooks’ actions, officials told media over the weekend. [...] After Crooks was killed, multiple news outlets have reported, a photo emerged of a law enforcement officer standing above his body. In the image, which NPR has not independently verified, Crooks is seen wearing a gray T-shirt from Demolition Ranch, a YouTube channel that features videos about firearms, demolition and experiments with guns. [...] Investigators are working to put together what may have motivated Crooks to target Trump. They are looking into his actions in the days and weeks before the shooting.