RR,
Not sure what delayed the investigation means.
I have significant experience in underwater recovery.
There are many factors, when even if you know the surface impact point, determine the search grid and potential bottom location.
I understand the depth of the 447 was substantial. This in itself, leads to quite a bit of research to ascertain the bottom location. All of the materials will ave a relative density as in relates to the seawater. The seawater also has bands of density in relation to currents, temperatures, salinity, and MET factors. Surface conditions at the time of impacts need to be considered as well.
The oceans have different describable levels, as levels of dense, cold water, will migrate, much as the currents in the air. Pilots are aware of all of the different layers of air, temperature, and density, and the gulf stream affects, the same is true of the underwater 'currents', nothing is ever static.
You mentioned the 'aluminum shower', well the debris field can be theoretically calculated, but as we have all noted in the Titanic, that mass took quite the effort to find. The pieces of the aircraft would have a relative density to the seawater on descent, not to mention the buoyancy effects of the shapes in flutter. Given that, the denser, less aerodynamic pieces, would tend to descend rapidly, hence, more directly straight down, and due to pressure at depth, would potentially accelerate at the same rate. I believe what we are seeing in the underwater images, is all of the 'pieces' of the near the same relative aerodynamic density with regards to the descent.
To me, this means that the impact of the vessel had little forward momentum, as the density of impact, had there been significant forward motion, would have left assemblies of relative density along a trail.