evidence: Eyewitnesses who spoke to CNN on Saturday described an awful scene following a shooting at former President Donald Trump’s rally in Butler, Pennsylvania, in which one person was killed and two others injured in what’s being investigated as a possible assassination attempt. [...] A law enforcement source and a police officer at the scene told CNN the shooter was positioned on a building rooftop just outside the rally venue. The source said the building was the same one where CNN had seen a heavy police presence following the shooting. The building would have been to Trump’s right as he spoke. [...] "I was at the far right of the podium, where the people sit in the front. I was filming him (Trump) speaking on my phone. Just as I was panning back, I heard seven gunshots in rapid successions, in under two or three seconds," Meyn said.