"Infinite justice" made no sense as a brand name for an operation to attack Afghanistan because human justice is both finite and fallible. More importantly, it begged the question, which our leaders must urgently address, of exactly what "justice" they propose to afford their prime suspect. The saloon-bar poster ("Wanted: dead or alive") invites lynch law: righteous anger requires that Osama bin Laden be treated according to international law. That law, it must be acknowledged, justifies breaching "state sovereignty" – the refuge of scoundrels like Pinochet and Milosevic – when force is necessary in self-defence or to punish a crime against humanity.
The International Court of Justice declared in 1949, in a ruling sought by Britain when its ships in the Corfu Channel were attacked from Albania, that every state has a duty to prevent its territory being used for unlawful attacks on other states. In 1980, after the hostage taking at the US embassy, the same court ruled that Iran was responsible for a failure in "vigilance" and a toleration of terrorism. It follows that the right of self-defence (preserved in Article 51 of the UN Charter) permits the US to resort to force for the limited purpose of doing Afghanistan's duty, once that state refuses to prosecute or extradite Mr bin Laden, and to close down his camps.
But America's legal right is severely qualified: the military exercise must have justice as its sole objective – by arresting terrorist suspects, gathering evidence and destroying weapons and training camps. On no account must it target civilians. The precedent which places the severest legal limit on the US attack was established by its own protest against Britain's sinking in 1837 of a US steamboat which was aiding rebels in Canada: both governments agreed self defence must be based on a necessity which is "instant, overwhelming, leaving no choice of means, and no moment for deliberation".
A more modern and more permissive legal justification for an armed response is provided by the emerging human rights rule that requires international action to prevent and to punish "crimes against humanity". The black Tuesday atrocities precisely fit the definition, which covers not only genocide and torture but "multiple acts of murder committed as part of a systematic attack against a civilian population". It was to punish such crimes in Kosovo that Nato breached Serbian sovereignty, and the same principles should apply (this time, with Security Council backing) to any intervention in Afghanistan. But this means the US must acknowledge that organised terrorist groups (including those it has supported, like the Contras) as well as states, are capable of committing such crimes.
Whatever basis America and its allies advance for their "war", the $64,000 question is whether they are entitled not only to hunt for Mr bin Laden but to bring down the Taliban government. This wider purpose, signalled yesterday by Tony Blair, only becomes lawful if Taliban forces attack a Security Council approved mission to arrest Mr bin Laden. So long as that US-led force confines itself to doing what the local government ought to do, any attack upon it directed by that government entitles the allies to strike back – to declare a "just war" and to overthrow the Taliban.
But this all depends upon whether, at this initial stage, the US and its allies are preparing to breach Afghanistan's sovereignty with the legitimate objective of bringing Mr bin Laden to trial in a court that can guarantee him justice. It is this dimension which must now be honestly addressed, because the plain fact is that a jury trial in New York, with a death sentence upon conviction, will not provide a forum where justice can be seen to be done. It may be doubted whether any American jury could put aside the prejudice against the "prime suspect" created by its media and by its leader's demands for his "head on a plate". The only "guilty" verdict which can persuade the world of Mr bin Laden's guilt will be closely and carefully reasoned, delivered by distinguished jurists, some from Muslim countries.
There is such a criminal court in session at The Hague, dealing fairly and effectively with crimes against humanity committed in the former Yugoslavia and Rwanda. The Security Council would undoubtedly agree to any US request to extend its remit to try Mr bin Laden. The Hague Tribunal affords all basic rights to defendants, in trials before three international judges and appeals to a further five. It has developed reasonably fair procedures for evaluating the kind of hearsay evidence which may be necessary to prove terrorist conspiracies, and has protocols which protect the security of electronic intercepts and other fruits of secret intelligence gathering.
The alternative is to construct a special Lockerbie-style tribunal, or even to bring the International Criminal Court hurriedly into existence with a retrospective mandate to deal with terrorist crimes against humanity. The existence of such a court would obviate the problem President Bush now faces from demands to produce the proof of Mr bin Laden's guilt: this is the function of a prosecutor, who obtains his indictment – the warrant for arrest and trial – after presenting prima facie evidence to a judge.
But the creation of the international criminal court has been opposed by the Pentagon and right-wing Republicans, fearing it might one day indict an American soldier. This self-indulgent isolationism may no longer prevail if their nation comes to realise that punishing its enemies requires international co-operation. After all, we owe the idea of international criminal justice to President Truman, who insisted on the Nuremberg trials against the opposition of Churchill (who wanted the Nazi leaders shot on sight). He did so because "undiscriminating executions or punishments without definite findings of guilt, fairly arrived at, would not sit easily on the American conscience or be remembered by our children with pride".
It needs Mr Blair to remind the President of how "the American conscience" once cooled the British desire for revenge and created a court whose judgment stands as a landmark in civilisation's fight against racially motivated terror. Its legacy requires the Taliban government to extradite Mr bin Laden – for the crimes of 1998 as much as 2001 – but only permits the use of force if those who deploy it can promise him a fair trial. Without that guarantee, "operation infinite justice" becomes the cry of the Red Queen in Alice's Adventures in Wonderland: "sentence first – trial [posthumously] later".
Geoffrey Robertson QC is the author of 'Crimes Against Humanity: the struggle for global justice' (Penguin)