I'll be the first one to say, Its tough to gather anything from watching it. But... from what I can see;

- It looks like Charles is coming from the direction of the SUV as if he was in it when it arrived
- Charles was on a cell phone(?) when he sees the shooter running at him
- It looks like the shooter was already at the school
- Charles recognized the shooter and that he knew the shooter was coming with bad intentions.
- I would guess Charles did something to the shooter to make the shooter angry enough to want to kill Charles (Gang, Drugs or related to escort incident)
- This is all a HUGE misunderstanding, or Charles is on the wrong side of some shady stuff. My guess is the latter.

Take this all with a MAJOR grain of salt as its really all just opinion which isn't worth jack.