Let's think through the groups that might have done this.
AQ or similar: Boston marathon not a symbolic target, no claimed responsibility.
OWS types: marathon not a right wing or capitalist institution, no claimed responsibility.
Domestic right winger ala Chris Matthews wet dreams: Boston marathon not symbolic of anything they'd be pissed about, no claimed responsibility.
Random crazy person: not usually a group, no manifesto.
I mean, what does that even leave? Radical environmentalists?
It just keeps bugging me. If this was an ideological statement, there would have been responsibility claimed.
Dc snipers
Two dudes who just wanted to kill folks
True... But they weren't even competent to change cars. Something like this suggests a higher order of competence. I dunno...