What's unlawful about these enemy combatants?

What's in a word? When the word is "unlawful," quite a lot.

Early in June, in another major setback for the Bush administration's beleaguered military commissions, military judges in two trials declared that they lacked jurisdiction to try terror suspects detained at Guantánamo Bay.

Their holdings hinge on an apparent technicality. When Congress passed the Military Commissions Act of 2006, it only gave the commissions jurisdiction over "alien unlawful enemy combatants." The two suspected Al Qaeda members whose cases were at issue this week, Omar Khadr and Salim Ahmed Hamdan, had previously gone before Guantánamo's Combatant Status Review Tribunals, but those tribunals merely had determined that they were "enemy combatants," not "unlawful" enemy combatants. As a result, declared Army Col. Peter Brownback III and Navy Capt. Keith Allred, the military commissions lacked jurisdiction over them.

This may seem nitpicky, but it's not. Behind the rulings lies a major dispute about the status of the Guantánamo detainees. In 2001, the administration made a fateful decision to treat terrorism suspects as "enemy combatants" in the "war on terror" rather than trying them as criminals in civilian courts. This decision led to the current military commission meltdown. Here's how:

Generally speaking, it is illegal for ordinary people to kill other ordinary people. But the laws of war recognize that during an armed conflict, combatants on one side are supposed to try to kill combatants on the other side. If they are later captured, the opposing forces can detain them until the end of hostilities but can't try them for murder. They have "combatant immunity": If they killed opposing combatants, they were just doing their job.

What, then, is an "unlawful enemy combatant"? The Bush administration has long been fond of tossing around the phrase, but until the 2006 military commissions law, it had zero legal meaning.

The phrase arises out of the inappropriate conflation of two very different law-of-war concepts.

The first relates to the circumstances under which combatants can lose their combatant immunity. If a combatant kills an innocent civilian, for instance, it's a war crime, for which he can be tried. Loosely speaking, "unlawful enemy combatants" could refer to combatants who lose immunity by committing such crimes.

But the administration conflated this with a different law-of-war concept, that of unprivileged belligerency. Under the Geneva Conventions, combatants who fail to follow certain rules – such as those requiring the wearing of uniforms – are not entitled to be treated as prisoners of war if captured, a point the Bush administration has used to justify its decision not to grant POW status to detainees. But not wearing a uniform isn't necessarily a crime under the laws of war – if it were, many members of the US Special Forces, who often operate out of uniform, would technically be war criminals, along with civilians who take up arms against an invading army.

So let's come back to the Guantánamo detainees. In 2004, the administration created Combatant Status Review Tribunals in an overdue – and still flawed – effort to figure out whether the hundreds of detainees had been rightly detained in the first place. The tribunals identified some detainees who simply weren't enemy combatants, just people in the wrong place at the wrong time. Most of those detainees have been released. The remaining detainees were designated "enemy combatants" and will – in theory – face eventual trial before a military commission.

That's where we come to the heart of the problem, the issue that led the two judges to toss out the cases against Messrs. Khadr and Hamdan. Congress only gave the commissions jurisdiction over "unlawful enemy combatants." But the detainees have never been determined to have done anything that made their combatancy "unlawful," and, as Judge Allred noted, the definition of "enemy combatant" used by the earlier review tribunals was broad enough to potentially even include civilians not actively involved in hostilities. As a result, the judges concluded that they lacked jurisdiction to try the detainees.

Reading between the lines, it appears the judges thought that the Bush administration wanted to have its cake and eat it, too: Declare all terror suspects "enemy combatants" in a "war on terror" and also try them for actions such as seeking to kill US troops in that war. But you can't have it both ways; under the laws of war, if Al Qaeda suspects are combatants, it's not unlawful for them to kill US troops.

The real irony? While the military commissions have floundered, civilian courts have convicted numerous high-profile terror suspects. If the administration hadn't been so fixated on declaring "war" on terror, many of the suspected terrorists at Guantánamo might have been convicted long ago.

• Rosa Brooks is a professor at the Georgetown University Law Center in Washington. ©2007 Los Angeles Times Syndicate.