The Pic of "suspect #2" leaving the sean with his back pack on is amazing. Kind of hard to say he did it when you see that. Look for yourself:
But his conclusion at the end is just wrong. He points out that "the guy" does not have his pack after the bombs go off but that is just not true.
This picture ( in upper right) shows "the guy" standing there with his backpack:
But here is the full size, un-cropped version of the pic. You will see the bomb has gone off and on the other side of the finish line stands "the guy"... with his backback.