The Allies never pardoned Mengele. He escaped capture and execution due to a combination of bureaucratic bungling (he was captured by the US in 1945, and while in custody his name was added to a list of wanted major war criminals, but somehow the list never made it to the POW camp authorities until after they'd already released him), then the US government somehow forming the false belief that he had already died, then the obstacles Mossad encountered trying to track him down in early 1960s Argentina, then Mossad deciding that the security threat posed by the Arab states (in the years leading up to the Six Day War) was a higher priority, and that by the time (1985) that public pressure had built to the point that the Israeli, West German and US governments were motivated to make a serious effort to find him, he had already died (while vacationing under a false name in Brazil in 1979).
He escaped justice through ineptitude, lack of political will and competing priorities, luck, and the assistance of the Nazi underground, not due to any active decision to forgive his monstrous deeds.
He escaped justice through ineptitude, lack of political will and competing priorities, luck, and the assistance of the Nazi underground, not due to any active decision to forgive his monstrous deeds.