Its a difficult one. In school where were taught that the citizens knew of the concentration camps just not what went on in them or about the extermination camps.
Thinking about it they must have been aware of the concentration camps as not only millions of Jews but millions of gypsies, Jehovah�s Witness, political prisoners, homosexuals, Polish and other "un-desirables" where taken to the camps, not the sort of numbers to go un-noticed.
Also the Nazi party had been enforcing euthanasia on intellectually and physically disabled (wiki says 75,000 to 250, 000 of all ages were killed between 1939-1940).
I shouldn�t think the possibility that this kind of systematic murder could extent to others on the Nazi�s undesirable list could have been too far in the mind of German citizens?
Looking at the Wikipedia page on the Holocaust this is interesting:
�Debate also continues on how much average Germans knew about the Holocaust. Recent historical work suggests that the majority of Germans knew that Jews were being indiscriminately killed and persecuted, even if they did not know of the specifics of the death camps. Robert Gellately, a historian at Oxford University, conducted a widely-respected survey of the German media before and during the war, concluding that there was "substantial consent and active participation of large numbers of ordinary Germans" in aspects of the Holocaust, and documenting that the sight of columns of slave laborers were common, and that the basics of the concentration camps, if not the extermination camps, were widely known�
But there are plenty of cases of Germans helping Jews (and surely other Nazi targets). Living in a Nazi dictatorship must have been difficult to be openly repulsed by the camps, turning a blind eye will have been the easier than questioning from Gestapo.
Maybe the shame of not being able to do anything to help led to silence post war?