While it is likely this guy is a domestic nut since so far there's only been one gun involved...al Qaeda as a rule doesn't take credit for what they do- they're known for NOT taking credit. They have on occasion gotten bold enough to invent a nonexistant group and call in the name of the fake group, as they did with the US embassy bombings, but often they don't take credit at all, and certainly wouldn't take credit for anything BEFORE they're done.
If it is foreign I wouldn't say it was al Qaeda but more likely, some palestinian group, since they are known more for sniper-style shootings and small stuff.
Now Fox says a local RUMOR is that he's a native-American/hispanic guy.