 In summer 1945, he was accredited by British Intelligence to obtain evidence for all four Chief Prosecutors at the International Military Tribunal at Nuremberg.As a member of the British prosecution team, he cross-examined former German Field Marshal Gerd von Rundstedt during the trial.Calvocoressi later advised the US Chief Prosecutor (General Telford Taylor), who had been his Bletchley colleague, in some of the American follow-up trials (1946–1949).