My grandfather was in the Boston Marathon a couple times in the 80s and 90s, and I still have a lot of family back there. Regardless of who did it, hopefully this doesn't drag us into another war, we simply cannot afford it at this point; and hopefully more of our civil liberties won't be sacrificed, because we simply cannot afford it at this point.
The crazy thing is, I have always said if the TSA has the right to check us at airports, they have the right to check us as well travel down our roads or walk down our sidewalks, just as likely for a bomb to be set off in these instances. Hopefully the TSA goons won't be on every corner now.
I think it will an "Iranian terror cell" or "White Supremacists", just a guess. Maybe the North Koreans, but that doesn't seem highly plausible or logical for them to pick that specific target.