To me the obvious reason is the null hypothesis: in the US law enforcement officers don't actually have the standard operating procedure of "putting a few bullets" in people for "resisting arrest". The alternative hypothesis is a double conspiracy theory, that they are generally cold blooded killers, but in this case for some whatever reasons, they didn't shoot the Boston bomber, but rather they kept him alive to make an example out of him? I don't know, this doesn't pass any type of smell test to me.
