I think its all 3. Some nut job terrorist that is operating domestically
No matter what the issue, these morons fail to understand that you get more honey than you do with vinegar to attract attention to your cause. Blowing up either the honey OR the vinegar gets you negative focus 100% of the time but doing it in a place like this, hmm...doing it in a place like this is intended to draw the public into fears of similar events happening at their local YMCA or parade or school. The scary part is if this was a terrorism bit, why was it not caught? Is this a new threat we don't know about and this is their "hey ya'll we'sa here to make life hell" or even scarier, is this the act of one or 3 people who have done nothing to signal any such events. A small enough, quiet enough group to make it almost impossible for the alphabet groups to find. Recall the DC sniper. They really only got caught because they got lazy, not because the LEOs were one step behind them.
Right now I'm not thinking anything. Just praying not too many got hurt.
Would care not to speculate for the next three weeks while they investigate what happened.
It only happened hours ago and I'm already tired of the media speculation.
FYI - Cell phone service has been shut down in the Boston area in an effor to prevent cell phones from accidently detonating any more bombs. Landline is the only form of working telephone communication at the moment.