"Now they don't know why he stopped shooting at the crowd. Nothing about this made any sense before, and it still doesn't."

Maybe he stopped (if he ever really started) because somebody else .... Neutralized, Assassinated, Terminated, Liquidated, Taken out, Removed, Rubbed out, Wasted his duppa !

Then he .... Assumed room temperature, Went Belly up, Vacationing in that mysterious place after death, Bit the dust, Bit the big one, Breathed his last, Bought the farm, Dead as a door nail, Dead as a Dodo, Snuffed out, Went Tits up, Counting worms, Slipped on his pine overcoat, Kissed his arse goodbye, Sucking face with the Grip Reaper and finally .....He Cashed in his chips . Heheheheheheheeheee

Basically, he stopped because someone Wacked him to throw a wrench into this whole mess !