"Actually, according to Airbus confidential drawings (thank you Mr google) the whole tailcone subassembly is bolted to the rest of the empennage via attachment lugs at 4 points. None of those large lugs is visible in the crash photos. In TylerMonkey's photo (#581) showing "better detail" of the tailcone front firewall, the location of 1 of the missing lugs would be expected in the top left of the photo - in the position of the triangular hole in the outermost frame."
The lug attach areas are visible, and have obviously failed in tension. The support structure is pulled out and missing. The only fitting still present appears to be an alignment hole at the top.
As to the aft part of the fuselage breaking "clean", it is a skin failure just as I described. Go to the Greek site with the high res pic of the back door area. You can see where the skin tore cleanly at the top of the fuselage, it cracked and broke at the first rivet line, the rivets did not fail. About an inch or so of the skin joint is still attached to the rear frame.
The stringers failed just forward of their rear attach points, again no rivet failure.
That area of fuselage broke away from top down due to overstress in tension. Aerodynamic tail downforce or internal pressure can not be determined from the pic, but a good guess can be made,