One of the hopes of a more enlightened rule of international law is the turning away of the world from the death penalty, even for the most serious crimes of genocide. From the Nuremberg trials of 1945-46 to today's apparatus for dealing with war crimes based on the international court at the Hague, one of the profound shifts in legal attitudes has been the gradual disavowal of capital punishment. Even Israel, which executed Adolf Eichmann in 1962, would not use the death penalty again.

The principle underlying this shift is a powerful one that should be applied consistently: that the deliberate taking of a human life is a crime. It cannot be right, therefore, to punish a crime by committing another. Ultimately, nothing can resist the force of that argument and eventually the death penalty will be outlawed all over the world. But not, yet, in Iraq, or in most southern states of the US.

Thus Saddam Hussein's execution was inevitable from the moment he was pulled out of a hole in the ground in December 2003. Inevitable, but wrong. It would have been possible for Saddam to have been sent to a third country - the Hague in the Netherlands presented itself as the obvious location - and have him tried by a UN war crimes tribunal. That was what happened to Slobodan Milosevic, the former Serbian leader, who died of natural causes earlier this year while on trial before a UN court. Or Saddam could have been tried by a UN court in his own country. That was what happened to Foday Sankoh, the leader of the arm-chopping Revolutionary United Front, who died of a stroke in jail in Sierra Leone in 2003 while awaiting trial by a UN war crimes tribunal there.

The trouble with those options, from the American point of view, is that the worst punishment available to such courts is life imprisonment. We do not suggest that George Bush wanted Saddam to hang to satisfy the bloodlust of redneck US voters; it seems that the US administration judged early on that the former tyrant's demise would make the security situation in Iraq easier. How that decision is mocked by events: it is hard to see how another drop of blood in the sea of carnage that is Iraq today will make the slightest difference.

However, it was President Bush who decided, in effect, what was to happen to Saddam. He decided to follow what might be described erroneously as the Pinochet model - of having a former dictator face justice in his own country - the point about General Pinochet being that he was arrested in London on a warrant issued by a Spanish magistrate. Until he was sent back to Chile as medically unfit to stand trial, the Pinochet case was an innovation in extending the extra-territorial principle of international law. In any case, the idea that Saddam was tried by the robust legal system of an independent, securely democratic nation is a fiction. Chile, as a stable, democratic country that had made the transition from dictatorship, was clearly able to hold Pinochet to account, whatever one thinks of his medical excuses. Iraq is not in a similar position. The reason that it was President Bush who ultimately decided Saddam's fate is because it is he who wields what ultimate power there is in Iraq.

Despite a formal handover of sovereignty in 2004, the Americans still run Iraq - we use the word "run" loosely, in the sense that US military force remains pre-eminent in the Hobbesian anarchy. This was confirmed throughout Saddam's trial, which was guided by US advisers and which took place under US armed guard while the defendant was managed by US warders. And it was confirmed before Saddam's hanging yesterday, when the condemned man was handed over to notionally Iraqi custody only hours earlier.

Even with the Americans running the show, maintaining the semblance of a fair trial seemed, at times, a daily struggle. The mortality rate among judges, lawyers and witnesses was appalling. This matters for the same reason that the recourse to the death penalty matters: because Saddam should have been held to account by a standard of justice that was manifestly not just higher than that over which he presided - not difficult - but the highest that the democratic world can offer.

Too much about Saddam's trial and sentence had the feel of expediency rather than the majesty of patient and scrupulous justice. The rush to execute him only prompts speculation about motives other than the dispassionate administration of the law. How much better it would have been, not least for the prestige of the United States, if it had handed over responsibility for trying Saddam to the UN. Not only would this have deflected some of the suspicion of America harboured by Arabs and Muslims throughout the Middle East, but it would also have avoided awkward questions about the support of previous US administrations for Saddam. A UN tribunal, whether in Iraq or the Hague, would have been able to appeal more convincingly to the authority of universal rights.

It is vitally important for the development of international law as a real brake on the ambitions of tyrants around the world that crimes against humanity be prosecuted with consistency and respect for procedure. Dictators should feel the chill of international law, whether they are surrounded by their guards in their palaces, or on a trip to a London clinic after retiring in luxury. They should fear what might happen to them after they have been toppled, legitimately or otherwise.

But the trial and execution of Saddam will do little to add to the force of international law, which derives from its high-mindedness, because it was such a flawed process so closely identified with the occupying American forces. As we saw yesterday, it can too easily be portrayed not just by Sunni sectarians in Iraq but by anti-Western opinion throughout the Arab and Muslim worlds as victor's justice.