Lawprof John Barrett passes this along:

[After the end of the War in Europe,] Justice Jackson was working by appointment of President Truman as United States chief of counsel to bring about the trial of suspected Nazi war criminals. In July 1945, Jackson was in London, negotiating with the United States's British, Soviet and French allies in an attempt to reach an agreement that would create an international military tribunal and define crimes and legal procedures that would make it possible actually to conduct such trials. By early July, the negotiations had been underway for some time and were not going well.

On July 4th, after a difficult morning meeting at Westminster's Church House, focusing on issues that included the possibility of holding trials in Nuremberg, Germany, and the process by which these national representatives should try to draft a potential agreement, Jackson suddenly asked to be excused for the remainder of the day. It was time, he explained, for him to join in his country's annual celebration of "hostility toward the British" -- a remark that drew the first Soviet smiles of the negotiations. . . .