In this video that the FBI released Dzohkhar's backpack disappears behind him twice; at 0:5 and 0:27. The photo in question conveniently is taken from the same angle. Furthermore, it seems unreasonable that a 6 quart pressure cooker could hide behind such a small frame. Also, how could he bounce around so lightly with a 30lb pack hanging off one shoulder? Tamerlan is also in the photo in question just behind Dzohkhar. I don' think the photo proves anything either way.