In the light of murders, drug wars and other recent acts of violence, Keith Humphreys, PhD, has written an incredibly compelling post discussing what happens to people when they witness terrifying events and how they might be helped. He uses personal experience to illustrate his point (and it is not for the feint of heart):
Many years ago, my wife and I were driving home at night on Highway 101 and saw something that we wish we could forget, but never will. An apparently intoxicated man was walking slowly across the interstate, and the car next to us hit him at full speed, having no chance to stop or swerve when the man suddenly became visible in the headlights. The man was thrown high into the air and landed on the highway, to be immediately run over and killed by the car behind us. I write about this horrific experience now to tell you what you might expect if you ever experience a traumatic shock and how you can help someone else who has been through one.
My wife and I illustrate the extremes. She began screaming as soon as the man was struck and thrown into the air, while I just stared silently, as if I were watching a movie from the very back of the theater. As he was run over a second time, I heard the sound of his head being struck by the bumper and his body being crushed into pavement by the undercarriage. With windows rolled up and the second impact taking place as we were already past the spot of the first collision, hearing that sickening impact - like the sound a bowling ball makes as it comes out of the return chute and collides with the other balls - would have been impossible, yet in my head I heard it. I turned to face directly forward, gripped the wheel tightly and stared into space, dimly aware that my wife was yelling somewhere in the distance.
The rest of his entry is, while frightening, definitely worth reading.