Fifty years ago this August, Charles Whitman ascended UT-Austin’s iconic tower and unleashed a shooting spree that left 14 dead and more than 30 injured on the mall below. This hour, we’ll revisit that day and hear the stories of ordinary people who displayed extraordinary courage, the subject of the documentary “Tower.” The film screens Tuesday night at the Dallas International Film Festival, and we’ll be joined by its director, Keith Maitland, and Claire Wilson, who was struck by one of Whitman’s bullets.