Photo: David Guttenfelder/The New York Times/Redux Before a bullet turned Alex Pretti into a symbol, he was a human being and a nurse. He had spent years working in the intensive-care unit of the VA Medical Center in Minneapolis, where he was responsible for the sickest and most badly injured veterans in the hospital. Within hours of the killing by Border Patrol agents, Mac Randolph, a local man, shared a video of Pretti on the job. In it, Randolph’s father has just died, and his body is draped