Quoting the BEA:
The forward and aft parts of the airplane are broken apart and mixed up, which means that a time-consuming systematic search is required.
The wreckage was found to be mixed up. I wonder, could the aircraft after its initial relatively flat impact have bounced and cart wheeled on the ocean surface, mixing the wreckage at that time, or did the mixup occur during its 3,900 meter descent to the ocean floor? If it cart wheeled, the CSMU's trajectory after it broke loose may have been such that it was thrown some distance from the rest of the tail section before starting its descent (and the same goes for the APU). It may also explain why the engine found was detached from its pylon.