I fail to see how there can be any conspiracy about it. Every argument I've read saying it's a conspiracy can get refuted if you've done your research. Like the one with that principal at Sandy Hook; I can't really disprove that for I didn't watch it, but did that person ever think that maybe they were referencing her? The words on the screen don't always go with the image and Newport is pretty close to Boston, so maybe Donna was running the marathon in honor of her?
The only conspiracy that I can understand is why was the backpack black when Johar had a white backpack. My two theories are that it's either Tamerlan's backpack (he had a black one) or when it exploded the backpack went inside-out, showing the black interior instead (don't even know if that's possible but it's only a theory of mine).
On a related note, Johar is telling them that the attacks were inspired by religion (no surprise) and that they were defending their faith. There's still several unanswered questions but at least he's talking.