I am starting to get a bad feeling about this. I am not one who is given to conspiracy theories, but this would be just a little too pat, wouldn't it?
After this outrageous bombing, the authorities catch the subjects with some assault rifles bought illegally, but whoops! They were both killed resisting arrest.
"Give us your guns now or you support the Boston terrorists!"
Let's employ Occam's razor here.
Shoot a cop, kill the cop, continue to fire at other cops, get shot in return, die.
Chances of conspiracy - 0%.
Chances of people who are prone to magical thinking alleging a conspiracy exists - 100%.
unknown how weapons obtained at this time ... the explosives would be illegal and activity of the two being sought proves illegal activity. Understand your thoughts and I will let this all shake out before final thought.