There are voluminous amounts of testimony from tens of thousands of survivors of the Holocaust, as well as the testimony of captured Nazi officers at the Nuremberg Trials and other times. Höss's testimony did not consist of merely a signed confession; while in jail he also wrote two volumes of memoirs and gave extensive testimony outside of the Nuremberg proceedings. Further, his testimony agrees with that of other contemporary written accounts by Auschwitz officials, such as Pery Broad, an SS man stationed at Auschwitz while Höss was the commandant and the diary kept by SS physician at Auschwitz Johann Kremer, as well as the testimony of hundreds of camp guards and victims. In addition, former SS personnel have criticised Holocaust denial. SS-Oberscharführer Josef Klehr said that anyone who maintains that nobody was gassed at Auschwitz must be "crazy or on the wrong". SS-Unterscharführer Oswald Kaduk stated that he did not consider those who maintain such a thing as normal people. Hearing about Holocaust denial compelled former SS-"Rottenführer" Oskar Gröning to publicly speak about what he witnessed at Auschwitz, and denounce Holocaust deniers, stating: