I don't think it is illogical to consider that this might be 'islamic' terrorists. (It is clearly terrorism, whether or not it is islamic or not.)
My theory is that it is tied to 'islamic' terrorists. This is partly because of the location (DC area) as this has maximum effect on people in DC. They can't take that leisurly stroll from one building to another in DC without thinking about this stuff now, and looking around for any white vans or suspicious persons (whatever that may mean.)
Further, it is consistent with the Al Queda training tapes that were found recently wherein these exact sorts of scenarios were laid out and trained for. Whoever is doing this has some degree of marksmanship skills, and a heart of stone. There would have to have been some planning involved in choosing escape routes, or else this person (persons) are just extremely lucky there have been so few clues/witnesses.
Lastly, I know that a component of my thinking that it is 'islamic' terrorism is related to my hoping that it is not a 'white male gun owner' as some of the profiles have indicated ... because I am a white male gun owner, and I hate being painted with that brush, even tangentially. But wishful thinking on my part does not make it any more likely that it is 'islamic' terrorism.
It could be anyone -- lone nut, extreme lefty/righty, sociopathic spree killer, islamist terrorist. I just hope that whoever it is slips up or runs out of luck quickly, and we find out for sure who and why. And if it is in fact islamic in nature, then we all need to know this to better prepare ourselves when and if this eventually hits our own communities.