After reviewing the side shot over and over, there's a couple things bothering me. There is zero question the man in white releases a projectile towards Charlie. It doesn't appear to be a lethal object but the timing is too exact to be a coincidence. Everyone of these people, from the Zin dip shit, the coffee shop guy w/the rifle up on his dash, all of them are 'accessories' as far as I'm concerned. As for the guy running w/pistol drawn, he should be identified but I'd assume he's law enforcement. It's typical for an event to offer 'overtime' for off duty cops to attend events like this so that's my uninformed assumption.
It's fired from the man in white, you can track in VLC by watching it in painfully slow frame by frame. I don't think it's a bullet, I think it's one of those plastic pellet things similar to airsoft. The timing is to perfect to be a coincidence though.