If there is a truth which the world now holds to be self-evident, it is that the US prison camp in Guantánamo Bay should close. Four prosecutors at the camp have resigned, and the last one to do so, Darrel Vandeveld, could become a defence witness. He claimed the US government was not providing lawyers with material that might be important in mounting a defence, and he is in a position to substantiate that grave charge. The camp, an international symbol of abuse and bungling, has become an open wound which continues to bleed.

But how to close it? The prison population of 255 can be divided into three groups: those against whom admissible evidence exists, (estimates of what the US defence secretary, Robert Gates, described as the irreducible minimum range from 40 to 70); those who will ultimately be sent back to their country of nationality (a group of about 150); and the rest, who will be released. The first group provides the most difficulties, but not necessarily legal ones. If evidence exists - which is not based on water-boarding - it should be heard in a US federal court or by a regular court martial. Such evidence does exist in the case of Khalid Sheikh Mohammed, who confessed to masterminding 9/11. What the US has tried to spare itself by not trying such prisoners in open court is embarrassment about their treatment. But as a lawyer himself, Mr Obama will be more concerned by issues of due process than he will be frightened by the revelation of the US military's grimy secrets. He may indeed wish to see the facts emerge in open court.

Geoffrey Robertson QC suggested in a recent lecture that those who cannot be tried in the US or sent back to their country of nationality could be released under surveillance conditions - a form of house arrest which allows some freedom. The bigger question is how the US should atone for the use of torture under Donald Rumsfeld's watch. This, Mr Robertson argues, could be done by ratifying the torture convention and by waiving the right to keep Red Cross prison reports under wraps. Regular visits by the humanitarian organisation were used by Mr Rumsfeld as a cloak of respectability, a sure sign that torture was unthinkable. But its reports documented maltreatment, and had they been made public, abuses such as the ones highlighted in Abu Ghraib could have been stopped earlier. The Red Cross says the loss of confidentiality would deny them access to states which hold prisoners of war. But the US could take a lead that other states could follow.

Closing the prison camp at Guantánamo Bay will be messy. But close it must, if America is to restore its reputation as a nation which respects the rule of international law.