Here's the best theory I've heard.
According to a talking head on CNN or FOX( can't remember) there is a video game out in which the object is to act as sniper with one shot per victim and get a cross section of folks. According to him the sniper is probably 2 loser kids playing the game for real. There is a Tarot card element and the game ends with the phrase ' I Am God"
If such a game exists then my bet is it is Kids taking the game to i'ts full conclusion.
As for the long range shooting, I do not believe any special skills are involved out to 200 meters with an AR15 or Mini 14.
The White Van at the shooting the other day was SPEEDING AWAY from the scene. so I think the ATF stuff about the person waiting for a white van before shooting is misleading.
Bob T