During the Holocaust, a Jewish woman exposed up to 3,000 hiding Jews to the Gestapo to save her family. Even after the Nazis sent her parents and husband to Auschwitz anyway in 1943, she continued to work for the Gestapo until 1945.
After WWII, a group of Jewish "Avengers"formulated a Holocaust revenge plan to kill 6 million Germans by poisoning the water supply of many German cities. However, it was foiled by British police while the poison was in transit.
The SS officer who captured Anne Frank and her family became a member of West Germany's intelligence service after WWII. He bought Anne Frank's book to see if he was mentioned.
In Auschwitz, an SS guard fell in love with a Jewish prisoner. He saved her life multiple times and she testified on his behalf during his post-war trial.
John F Kennedy had such concerns about the space program's high cost, that he proposed partnering with the Soviet Unionon a joint expedition to the moon