The GI's who liberated the camps were certainly convinced. That and the horrific movie/photo evidence, mass graves, emaciated prisoners, gruesome collections of gold teeth, hair... and the ovens, ought to be enough to convince anyone. Those on trial at the time did not so much deny as whine they were "...only following orders."
A former girl friend wrote one of the books on the rescuers, ordinary people from many nations who risked their own lives to help Jews escape.
This is a link to an article from the German Publication "Der Spiegel" about Adolph Eichmann's life in Argentina before the Nazi hunters caught up with him. Apparently, when he was in his cups he would brag about what he had done... regretting nothing but that they hadn't killed them all.
http://www.spiegel.de/international/...-a-754486.html