unless you really think that the sniper is an islamic terrorist, which I find highly unlikely
Yeah, I don't think he's an Islamic terrrorist. Here's my take.
1.) The "Mr. Policeman, I'm God" tarot card business.
That "I'm God" stuff is more characteristic of an American or at least a Western young guy, say teenage to late twenties.
2.) If you look on any maps of where the shootings take place, it obvious he's a beltway bandit. I.e., the beltway is his stomping grounds, along with the major highways that radiate off of it. He is very familiar with driving around in these areas.
3.) He has so far not shot anybody on a weekend, which gives the impression he can't operate on a weekend.
4.) He using a vehicle that would stand out like a sore thumb in any dwelling where he had neighbors next door.
My conclusion is that he and his accomplice(s) might be the son(s)
of upscale professional couple(s) working in some sector related to the DC government, i.e. lobbyist, contractor, (or who knows? maybe a Senator or Representative?) He doesn't shoot on the weekends because that's when Mom and Dad are home. Mom and Dad probably live in a secluded area free of immediate neighbors. Mom and Dad are probably so busy and out of it that they don't even know if he has a friend with a white van, or that he been taking shooting lessons recently.
Just my take.