Visual analysis is quite interesting to me and there are usually more clues than first observed. Some mentioned lack of a bulge ring to indicate an obstruction. Yet there is a large section missing between the fore and aft ends of the rupture point. If you look again at the second picture from the OP, the top rib has tracks left from the exiting metal. The exact rumpture point can be easily seen as well as the direction of the departing pieces.

John