What's interesting is that in today's world a rational person's first go to assumption would be that any terrorist act is likely to have been committed by Islamic Fundamentalists. Now that doesn't mean that we should go out and condemn Muslims before the evidence is in but it does mean that in the absence of evidence speculating that conservatives are to blame says more about the bigotry of the left than it does about the nature of the terrorists.
Just as atheists ignore all violence by atheists--Stalin was an atheist and he was trying to crush religion in the Soviet Union but his mass murders say nothing about atheism--liberals tend to wish away all violence by liberals. In the minds of liberals if OWS participants rape women it's nothing and if an abortionist like Gosnell kills babies that were born alive it only shows why abortion should be legal--go figure--but if the one member of the Tea Party says something bad all Tea Party members are monsters.
While this atrocity may have been perpetrated by anti-government churls, it is Tax Day after all, historically anti-government extremists have gone after the government. McVeigh didn't park his truck bomb next to a Walmart for example. Islamic fanatics do tend to go after civilians rather than the government however.
We'll find out eventually but for now keep your eye on the liberal pundits who will try to blame anyone they don't like. It'll help you learn how the media works and how important the unconscious biases of the media are in shaping the "objective" news we hear from the Main Stream Media.