I've been to a lot of motorcycle races and only witnessed one (double) fatal accident in person. It was similar to that one where the guy was stranded in the middle of the track and tried to signal the other riders before getting hit. I'll never forget the sound of the bikes colliding and the lady next to me screaming. I was standing in the old tower that used to be at the start finish straight at Laguna Seca. I think I caught it on camera, but I've never gone back to look at it.
I bet the lady screaming made the situation much better and alleviated a ton of the stress and tension.