On Friday night, three prisoners in Guantánamo Bay committed suicide. Two Saudis and one Yemeni hanged themselves. In a desperate attempt at spin, the US claims this was an act of war or a public relations exercise. The truth is quite different. Islam says it goes against God to kill yourself. So what would drive a man to take his own life, despite his religious beliefs? The answer shames the US and its allies, Britain prominently included.

The 460-plus men in Guantánamo Bay have been held for longer than four years. Only 10 have been charged with a crime. Not one has had a trial. The men are not allowed to visit or speak with family or friends. Many have suffered serious abuse. Most are held on the basis of triple and quadruple hearsay, evidence so unreliable that a criminal court would throw it out. Yet the US says it can imprison the men for the rest of their lives. Imagine yourself in this environment, told you will never have the chance to stand up in a court and present your side of the argument. What would you do if no one would listen, if you had been asking for justice for four years and had nothing in return? How hopeless would you become?

Of these three men, little is known. They were in Camp I, a maximum-security area where prisoners are denied even a roll of toilet paper. But we do not know the dead men's stories. While most of the men in Guantánamo have lawyers who fight for their right to a fair trial, these men did not. Until May, the US refused to even tell us who was in Guantánamo. But before it finally released the names of everyone there, the Bush administration secured passage of a law barring lawsuits by the prisoners held in Guantánamo. That means that at last we know the prisoners' identities, but can do nothing legally to help them. The men who committed suicide found themselves in just this legal black hole. They had no legal recourse, just the prospect of a life in prison, in isolation, with no family, no friends, nothing. They took their lives.

So what now? President Bush stated this week that he wants to close Guantánamo, that he wants to give the men trials. Well, let's have them - immediately. The US has had over four years to gather evidence against the men. Surely that is enough time to prove guilt. And now it is time to show the world the evidence. As Harriet Harman, the British constitutional affairs minister, said yesterday, Guantánamo must be opened up to review or shut down. Will Britain do what is necessary to make this a reality? Because this is about even more than the fate of 460 people, it is about whether the US and its allies will lead the world by democratic example, or whether they will continue to give lip service to human rights and open societies, while denigrating those cherished notions with their actions.

If the men in Guantánamo (and the other US prisons around the world, such as the one at the Bagram air force base in Afghanistan, where over 600 men languish in Guantánamo's hidden twin) did something wrong, by all means punish them. But if they did not, they must be sent home.

Mohammed El Gharani, our client at Reprieve, was only 14 when he was seized in a mosque in Pakistan. He was only 15 when he arrived in Guantánamo Bay. Already twice this year he has tried to kill himself, once by hanging, once by slitting his wrists. Let us pray there is movement by the US to finally do justice, before Mohammed, truly only a child, or anyone else in Guantánamo Bay commits suicide.

· Zachary Katznelson is senior counsel at Reprieve, which represents 36 Guantánamo Bay detainees zachary@reprieve.org.uk