If some of us dream of a "rulebook" governing international human rights and the behavior of states at war, Nuremberg was an extremely poor interpretation of that rulebook.
In the planning and discussion regarding war crimes done prior to the Allied victory, Churchill and the British consistently took the position that Nazi leaders, once identified, should simply be shot without benefit of trial. The American view, however, prevailed, that an evidentiary hearing, presided over by impartial judges, was called for.
As two centuries of American jurisprudence prove, justice is hard enough to achieve domestically, despite our Constitution with its guarantees of due process and other limits on the rights of the state acting against a defendant. Politics, which co-exists as a realm within states along with law and the executive, is the sole existing realm in international affairs; international politics, especially when it shades over into war, involves values the opposite of those we cherish in domestic affairs, and especially lauds force and fraud in wartime.
Nuremberg did not successfully solve the problem of how to conduct a fair trial in an international tribunal. In general, it was what we in the computer industry call a "kluge", a ramshackle solution tacked together in a hurry, with a lack of process and a fundamental lack of agreement among the judges and prosecutors of different nations as to how they ought to conduct themselves.
Most significantly, the German defendants at Nuremberg were being tried for several categories of offense that had no precedent whatever under international law. The major focuses of the prosecution were crimes against the peace, crimes against humanity, war crimes, organizations, and conspiracy. Of all these, only war crimes were a clearly recognized category under pre-existing international law.
War crimes jurisprudence was based on the Hague and Geneva conventions, and narrowly governed the treatment of foreign soldiers and noncombatants during wartime. Technically, the only war crimes committed by the Germans involved the treatment of Allied prisoners of war and of the populations of conquered countries. (There was an additional legal wrinkle in that Germany had repudiated the Geneva and Hague conventions; but at least at one time it had been a party to them.)
The crimes against peace counts of the indictment dealt with the German decision to "wage aggressive war." This was acknowledged by all at Nuremberg to be an "ex post facto" charge, meaning that the defendants were indicted for something that was not a crime until after they had committed it. Ex post facto criminal laws are completely impermissible under the U.S. Constitution; prosecution of the Germans for noncrimes goes very far towards undermining the legitimacy nof the Nuremberg proceedings.
The crimes against humanity count dealt with the Nazi treatment of the Jews and other groups. Because international law regrettably had always left a state entirely free to dispose of its own nationals in any way it saw fit, including murdering them, the Nazis were again being tried under an ex-post-facto law, to the extent they were being tried for the murder of Jews and others who were German nationals.
The murky "organizations" and "conspiracy" counts need not be dealt with at length here. The first was an attempt to put certain Nazi party organizations, such as the SS, on trial. If the organizations were convicted, any German who had been a member of one during the war would have been considered guilty, though not present at the trial to defend himself. The conspiracy theory, like similar theories in American domestic cases, required vague clouds of evidence to bind defendants together, instead of connecting them to specific acts they had ordered or carried out.
If you were flipping channels and happened on a TV show in which a prosecutor and judge conspired to convict a defendant of a murder they themselves had committed, you would conclude you were watching trash. Yet this is exactly what happened at Nuremberg, where the Russian prosecutors insisted on including a count accusing the Nazis on trial of having ordered the massacre of 15,000 Polish oficers at the Katyn forest. In fact, as many suspected then and as is known to be a fact today, the officers had been executed by the Russians during their occupation of Poland after the Soviet pact with Hitler. As Telford Taylor, one of the prosecutorial staff at Nuremberg, concedes in his recent Anatomy of the Nuremberg Trials, the Soviet presence went a long way towards undermining the legitimacy of the tribunal. The other judges resisted the pressure and their final verdicts made no mention of the Katyn massacre--not enough in itself, hwoever, to cleanse the result.
If the Nuremberg trials could not be honestly brought--and the result seems to show that they were not--what was the alternative? Simple murder, the shooting of captured Nazis out of hand as urged by Churchill, would itself have been a severe violation of international law and put the Allies on the same plane as the Nazis. Perhaps the accused could have legally been kept as POW's for some time, or (this is the best solution) tried only for crimes recognized under pre-existing international law, such as violations of the Hague and Geneva conventions. In any event, a trial that in many respects was a show trial, brought under ex post facto laws and with a murderer on the panel, was not a good commencement for the international law of human rights.