Some xenophobes and racists are confused these days. You see, the Boston bombers may be Muslim, but they're not from the Middle East.
In fact, they're literally Caucasian - from Chechnya, in the North Caucasus in the Russian Federation - an area for which the race was named. As Peter Beinart recently wrote in The Daily Beast, "You can’t get whiter than that."
The racists can take some solace in the fact that the suspects have (or, in Tamerlan's case, had) dark hair and dark eyes, and might look a bit exotic if you want to stretch it. And stretch it they will, in their need to condemn "the other". In their imaginations, if you're not Judeo-Christian, you can't be a proper white person.
But give the bigots a break: After all, most Americans would probably be unable to quickly point to Chechnya on a map. And that's a whole other sad (and perhaps somewhat related) issue.