2 occupy a white van. No weapons, no sinister elements inside. They are, however, in contact with a second vehicle. White van gets to the proximity of the next sniper shooting. Immediately after the shooting, the white van speeds off, intent on being seen--because it contains no weapons, no residue, nothing to appear sinister. It is the decoy. Don't need it. Since the media latched onto the 'white van' early on, just wait till a white van is driving through the area, find a target, take a shot and someone will report a white van driving away. (someone else posted this theory first)
I've been pointing out for a while now that IMHO the killer is using misdirection techniques. There is an very high, almost guaranteed likelihood that he's not driving a white van at all. Given the very high commonality of white vans of one sort or another, it's a simple matter to pick out a "good" place to shoot from in a high traffic area, wait for a white van to wander onto the scene, and then shoot whatever poor unwitting victim happens to be handy once the misdirection situation unfolds. In other words, the killer is choosing a SITUATION that's convenient, not a victim. This is much easier to pull off.
Misdirection is a very common magician's tactic to get you to look one place, when you should be looking somewhere else to see what's REALLY going on. Use of this simple tactic allows the killer get away with his crime while all the witnesses on the scene are looking elsewhere - i.e. where the media & police have told them to look (for a white van). They're playing right into this psycho's hands. He's probably laughing his sicko @ss off about all this white van nonsense, since it gives him easy cover. The white van is a "white herring".