Could be. By now, it seems obvious that the shooter(s)'s motive is to terrorize.
That doesn't rule out a white wackjob, in my view. But it doesn't rule out an Islamist terrorist cell -- from the Middle East, North Africa, Southeast Asia or, for that matter, America -- either.
There are reasons, I suppose, why the authorities wouldn't want to raise that spectre -- until they had to. But it amazes me that the mainstream media won't utter the words "Islamist terrorists". I've seen a few stories in the mainstream media that start to venture down the terrorism trail...but, while they speculate about "terrorism", they never speculate about the identity or motivations of the "terrorists".
This is like the anthrax story all over again. The media is infatuated by the story. Even moreso, because they understand guns far better than the science of bacteriology. And they love it that it might prove to be a right-wing NRA dues-paying gun-nut and militiaman. But, so far as any other possibility, well, they just don't want to go there...
I'm almost embarrassed for them...