While more can always be said, this fantastic answer from the FAQ by /u/kieslowskifan answers not your question, but the question of if the disappearance of the Jews was a state secret, which it most certainly was not. It was well known to the German population:
An excerpt:
As to German knowledge of the KL work camps, most certainly knew about their operation. The sight of forced labor prisoners became pretty ubiquitous in wartime Germany especially as the economy geared to total war. Nor were these type of camps a state secret as the Third Reich relished proclaiming that this was the fate of the Volksgemeinschaft's enemies. The state presented the wartime expansion of the KL served as both a means to win the war but also to silently keep its population in line. One of the more ubiquitous memories German civilians have from the war is the "clack-clack" sound of the prisoners' wooden clogs as they repaired bomb damage.