The reason it was so hard for Nazi war criminals to be caught in the first place is that the US decided the moral focus of the times had changed since VE Day and that Nazis were no longer the Big Bads for the world, it was now the Soviets and any Communist allies they had.
So they employed suspected and known Nazi war criminals to set up networks of other Nazis living in Communist countries, especially in East Germany.
While the recently-liberated nations, notably France, were conducting searches across Europe for the criminals who’d destroyed their countries, the US was making sure they wouldn’t be caught and was moving them completely out of Europe if things got too tense for them there. Look up how they hired Klaus Barbie, the Butcher of Lyon, and helped him escape when the French caught on.
So like thanks, US government