The strangest part of this is that they haven't found any large debris that could be traced back to the plane. If a plane breaks apart in flight, shit's gonna fall to earth. If a plane hits the ocean at speed, there's going to be a ton of debris scattered over a large area.
However if a plane is able to make a controlled ditch into the ocean and lands at a slower, controlled speed, it could remain relatively intact I would imagine. Just look at the Hudson landing. So if it lands in one piece more or less, eventually it's going to sink in one piece. This wouldn't leave much of a debris field on the ocean. Hence the reason nobody can find the damn thing.
However if this is what happened, why were no distress calls made? Why don't they have it's last known position? Why didn't people get off the plane once it was sitting in the ocean?