A friend of mine worked trauma yesterday and she said it was a good thing it happened where it did.
First, with the abundance of medical personnel present, victims were immediately attended to. She said that if there had been no medical people present and there was a wait for ambulances, many of these people would have bled out and the death toll would had been at least 2 to 3 times what is is.
Second, there was such a high concentration of camera crews both private and public, the chances are very good that something was caught on film. It just will take time to sort through all of it.
This woman is a pacifist and I was surprised at her answer when I asked her what they should do to this guy. Her answer. "If you had seen the blood and carnage I saw...two words..death penalty."