[CRedskinsRule]

Well,

I'll just keep with my current obsession, and say this was done by a NK sympathizer.

Now that everyone has shaken their heads and rolled their eyes:
things we know:
NK never ever acknowledges responsibility for their attacks.
K-Un wants to attack the US.
The bomb was a basic, ie not mid eastern quality, attempt.
Eastern seaboard attacks would never be missiles, because they couldn't reach them.

All that said,
It was probably a domestic job local to Boston political shenanigans.