Given the date and it being Boston (all that tea party symbolism et alia) I suspected domestic immediately. We'll see.

I think it was date plus location meets an opportunity to spread fear/destruction, not any deep-seated loathing for marathons.

JFK library, on the other hand... I don't even.

It's all so ugly, ugliness at the core, no matter what patterns are used to attempt to bring some notion of decision (decisions supposedly being rational, and therefore tether the ugly as the mind tries to make sense out of the senseless) and reason to an unreasonable act.