Rudolf Kastner was a quisling traitor who openly and unabashedly collaborated with the Nazis, and specifically with his smoking/coffee buddy Adolf Eichmann, who he was on intimate terms with and on a first-name basis, welcome to his office unannounced at any time.
You don’t need me to tell you any of this, it’s all documented in the Vrba-Wetzler Report, by Aushwitz escapees Alfréd Wetzler and Rudolf Vrba, who personally handed Kastner the report of what the Germans were doing to Polish Jews and were still planning to do to Hungarian Jews. As Vrba and Wetzler testified, Kastner ignored them and their report, refused to pass the information to Hungarian Jewry before the Nazis loaded them unto the trains to Aushwitz and instead buried the report and information.