Thursday marks the fifth anniversary of the day the US military flew the first of some 700 battlefield detainees from Afghanistan to Guantánamo. Some of those same men are among the 395 still held at Guantánamo today. None of the detainees has ever had anything approaching a fair trial. Only 10 have ever had formal charges laid against them. Many are reportedly held in near-total isolation, and over the years both camp staff and released detainees have reported highly abusive treatment at the camp.

Guantánamo is a stain on America's honor. Like the episodes of abuse at Abu Ghraib prison in Iraq, Guantánamo (rightly) affects the standing of the US around the world. Even President Bush recognizes the problem: He has expressed a desire eventually to shut Guantánamo down. He and Congress should work speedily together to achieve this goal.

Lives in limbo

But meanwhile, the US military has constructed additional "supermax" cell blocks there. It's true, plans are also under way to build courtrooms that may one day help reduce the number of detainees, though officials admit that only a small number of detainees will ever be tried there. And even these trials, held under the Military Commissions Act (MCA) that Congress passed last September, are the subject of court challenges that may take many months to resolve.

So the detainees' lives remain in limbo. They are still held in troubling conditions, unable to see a clear end to their situation and unable, for now, to see or challenge any of the US government's evidence against them.

This is a real problem for a nation that considers itself a nation of laws and in the past has worked hard to uphold the rule of law in the international arena.

One fundamental principle of the rule of law is that a government may deprive a person of his liberty only under conditions regulated either by its own national legal system or (in certain circumstances) under the international laws of war, primarily, the Geneva Conventions.

Under national legal systems, prisoners should normally be entitled to a timely and fair trial, at which they can see and challenge the evidence against them. Under the Geneva Conventions, combatants captured in war have no right to trial, but they must be kept in humane conditions and released to their home countries when the war ends.

After the US invaded Afghanistan in October 2001, it found itself holding thousands of men captured on or near the battlefield. The Bush administration declared that the "war on terror" it was fighting there was unlike all previous wars, and therefore these captives were not entitled to Geneva protections. In Iraq in 2003, by contrast, the administration said the Geneva Conventions did apply.

The men the US detained in Afghanistan fell into a legal black hole, and for many of them, the name of that black hole has been Guantánamo. Administration lawyers argued for several years that US jurisdiction did not apply there. Last June, the Supreme Court ruled that it does, but it also ruled that the detainees don't have all the rights of US citizens.

When Congress passed the MCA last September, it tried to define what rights the detainees have and what kind of a trial they're entitled to.

However, government lawyers say they're unwilling to disclose the evidence they have against many detainees in a courtroom. (This is why only a few detainees will be granted a trial.)

The US lawyers probably have some legitimate concerns about disclosing the sources of secret evidence. But it's also likely that they don't want to disclose the circumstances of the interrogations from which most of their alleged evidence was acquired.

Facing the moral challenge

The government's problems regarding Guantánamo remain unresolved. The MCA courts promise no speedy closing for the prison camp there. And the "war on terror" that has been used to justify those prisoners' detention without trial will probably never have the kind of clear end that – if they were regular prisoners of war – would allow their release and repatriation.

Guantánamo is also a major moral challenge for the American people. We need to find a way to close this camp of shame and shine a light on the abuses committed there so that they're never repeated.

The detainees against whom there is solid evidence should be tried, and if found guilty, incarcerated. Let's see and fully examine all the evidence. The rest should be released and given help for their rehabilitation after their years of dehumanizing detention.

Will the new Congress take up this task? I certainly hope so.

• Helena Cobban is the author of "Amnesty after Atrocity? Healing Nations after Genocide and War Crimes."