“The senseless murder of the Jews was an act that was so shrouded in secrecy that the populace had no idea what was going on.”
http://en.wikipedia.org/wiki/Responsibility_for_the_Holocaust
“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 but they did not know about the Final Solution and 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.[8] The German scholar, Peter Longerich, in a study looking at what Germans knew about the mass murders concluded that: “General information concerning the mass murder of Jews was widespread in the German population.”[9]”
Well, this is anecdotal, but my grandfather toured Buchenwald, right after it was liberated. He once told me that anyone who said they didn't know what was happening there is a liar, because you could smell the place from 20 miles away.