No statute of limitations on crimes like this
you could never prove he did anything. you could prove that he was 19. You had 70 years to find him guilty while he lived as a law abiding US citizen in the open, never denying who he was, where he worked.
This is very likely two wrongs. Even if one was much larger than the other. You cannot punish him. He lived his life. And unfortunately there will be no one in this world to punish the sanctimonious Nazi hunters who don’t care about due process.