The Nuremberg Trials were backed by the most force the world had ever known! And even then, the Allies wiped their ass with the rules (that they mostly made up ex post facto) and grabbed any Nazis that were useful and plenty that were not. Even putting aside all the Paperclip scientists, who absolutely knew what they were involved with, the US took plenty of SS officers - Otto von Bolschwing, Klaus Barbie, Alois Brunner, etc. Everyone violated their own “rules” left and right and occasionally, if they could be bothered, made up justifications later. This is not a controversial view: in fact the contemporary British opinion was that you can’t make up laws ex post facto and the Nazis should just be executed. The Soviets anticipated a show trial and their “judges” did nothing before phoning Moscow first. The Nuremberg trials were the 1940s legal equivalent of Calvinball.

To the mediators, I’m unsure why that would be an example. We’ve had mediators for a very long time and UN mediation is only the latest flavor of that.