Yeah, but that has its contradictions. If the point is to kill in a manner that there is no to track it back to you then you don't want something cool nor are you really going to brag - it is between you and your buddy. You have two bombs so that neither was in a position to be able to rat out the other. Just coming from there that town is full of college kids who are sure they know more than everyone else and are infallible. If all you wanted to do was kill you could do that at any shopping mall, but the placement of these bombs ensures they get great video for free from the internet without having to do anything other than download it like hundreds of thousands of other people. You and your buddy can watch it over and over again to your dark heart's content.
I guess I just can't see a good reason to attack this event. The day has meaning in both being tax day and Patriots day (and probably a hundred other anniversaries that have meaning to someone). But if it was tied to an attack on the US government by a homegrown group why not attack a federal building? The event is a international event but if that was your aim than why not attack when the winner was crossing the finish line? I am just not seeing a lot of international value to an attack four hours into the race. Plus no one is taking credit. Political terrorism is usually tied to some aim. It losses value if it is not tied to a cause or is not part of a larger barrage of attacks intended to cause widespread fear and panic. I guess I am not seeing a political or ideological tie in here. Seems murder is as good a reason as any.