I hear you, but given the reports of the kinds of injuries sustained by the bomb, it seems like the intent may have been to wound more than to kill. The bombs went off low and many people will likely have limbs amputated by the blast or have to have limbs amputated. On Boston's NPR they're saying that at least one of the people dead is very likely a child. As I mentioned in this thread, Boston is known for not being great on the security front, particularly at Logan airport and the various riots that have happened over the last decade among other incidents. A lot of my friends are in Boston and as far as I know, none of them are physically hurt, but I can tell you that terrorism or not, people are terrified.
No doubt, that was why I added the "incidental terrorism" part. Even if it wasn't a terrorist act, it still terrorizes as a consequence. Who knows what the offender's purpose was at this point. Could have been that he (gonna go ahead and assume that it was a "he") wanted to hurt rather than kill. Could have just as easily been that he was just kind of an incompetent criminal. Can't remember where, but I recall somebody trying to stash some pipe bombs in trashcans during an MLK day parade a few years ago. Had they gone off, not many people would have been hurt, but the guy's stated intent was to kill. My feeling is that some people just want to cause as much damage and grief as possible, and they're not too concerned with the specifics.