It might be almost any radical group-—But-—I do think the mass wounding, double bombs, Terror at a soft target seem to point to the Middle East—maybe payback for Drone attacks? Maybe something paid for by Iran? Maybe Egyptians hitting us for holding the Blind Sheikh they worship? Could be almost anything. The truth will come out—I only play its before they strike again.
Most likely a random Moslem individual or group of pals. No affiliation. Just like the other small-time bombers who failed. Times Square, etc. Probably American in origin, but not in culture.