[hef19898]

And the holocaust by bullets pre dates operation Barbarossa. Turned murdering millions of people requires more sophisticated logistics than your average, run of the mill genocide as all tjose done before. Hence Wannsee, the final solution, the extermination camps (of which Auschwitz wasn't one initially). The goal was clear from before the war started so, the means were somewhat less well defined.

Edit: As a supply chain and logistics guy myself, the logistics of the holocaust seem to be the only historical occurance the Germans got wartime logistics right. Eichmann was a really good supply chain guy, running a tremendously efficient operation from, and beware the following will be incredible cynical now, sourcing (getting jews concentrated in ghettos) with close collaboration of local suppliers (the SS, Gestapo and local authorities ranging from French police to the various collaborators in the east) over transportation (including Eichmann himself working on details like damaged passanger rail cars to keep his prime carrier, the Reichsbahn, happy) to the classification of people arriving in incredibly well run extermination factories in the occupied East. It is that efficiency, applied at murdering innocent people for a deprived ideology, that makes the holocaust stand out from all other genocides in history. And that was the main, if not even the only goal, of the Nazis behind WW2.