A single word added by Congress to define detainees eligible for military tribunals could end up resulting in those cases being tossed, based on the ruling Monday of a U.S. military judge in the case of a Canadian detainee at Guantanamo Bay, Cuba.

In a matter of minutes, Army Col. Peter Brownback ruled that charges against Khadr, who is accused of committing murder in violation of the law of war among other charges, must be dropped because he was not properly classified as an "unlawful enemy combatant" after being interred at Guantanamo and charged in 2004.

In 2006, President Bush signed into law the Military Commissions Act after the Supreme Court threw out the previous war-crimes trial system. The act states that only those classified as "unlawful enemy combatants" can face military commission trials on Guantanamo.

But none of the detainees have been defined as "unlawful" enemy combatants, just "enemy combatants." Prosecutors argued that Khadr qualified as unlawful because he fought for Al Qaeda and was not part of any regular, national army.

The chief of military defense attorneys said the ruling will have a "huge" impact on all the cases being brought to trial.

Brownback said he had no choice but to throw out the case.

"The charges are dismissed without prejudice," Brownback said as he adjourned the proceeding. He did leave open the possibility that a review board could come back and classify Khadr as an "unlawful enemy combatant."

Khadr was 15 when he was picked up in Afghanistan following a 2002 firefight in which he allegedly killed a U.S. soldier with a grenade. He too was wounded in the attack. He faced charges of murder in violation of the law of war, attempted murder in violation of the law of war, conspiracy, providing material support for terrorism and spying.

The dismissal of the charges does not mean Khadr, who appeared in the courtroom with a beard and wearing an olive green prison uniform, will be freed from Guantanamo. Only three of the roughly 380 men held on suspicion of links to the Taliban and Al Qaeda have been charged so far under the new military tribunal system.

The Associated Press contributed to this report.