The whole thing was a trial run to see what martial law would look like and how to go about handling it in a real world scenario, it was live practice for them to see how the public would react, what the public would tolerate.
What about the guys at the end of the Boston marathon wearing khaki pants and black jackets, wearing hats with the Punisher skull on it, also known as "Craft" contractors? One had a backpack, was in the exact area of the explosion, and a photograph of his exploded backpack was later taken. It wasn't Tsarnaev at all, it was govt. contractors plain and simple. Even police there at the end of the marathon were warning people not to panic even before the hoax event occurred. And yet again, the American public was lied to.