Observers say the ruling could prevent trials in the future by military commissions against some 380 other detainees at the U.S. military detention center.
On June 4, presiding judge and U.S. Army Colonel Peter Brownback said the military-commission system -- created last year by the U.S. Congress -- lacked jurisdiction in the cases.
The judge cited a military-review board's decision to label the detainees as "enemy combatants" rather than as "unlawful enemy combatants." The Military Commissions Act of 2006 specifies that the tribunal can only hear cases against "unlawful enemy combatants."
Still In Custody
One detainee, Omar Khadr, is a 20-year-old Canadian who was captured in Afghanistan when he was 15 and is accused of killing a U.S. soldier with a hand grenade.
Charges also were dropped against Salim Ahmad Hamdan of Yemen, who is accused of working as a driver and bodyguard for Al-Qaeda leader Osama bin Laden. Last year, Hamdan won a U.S. Supreme Court case that led to the scrapping of the first U.S. military tribunal system at Guantanamo Bay.
Both Khadr and Hamdan remain in custody at Guantanamo Bay as terrorist suspects.
U.S. Defense Secretary Robert Gates said in Bishkek, Kyrgyzstan, today that it is too early to comment on the implications the ruling could have on other trials against Guantanamo detainees.
"I just heard about this five minutes ago," Gates said. "I don't know the details of the ruling. If it is as described, that's the reason we have a judicial process in all of this and we'll have to take a look at it and see what the implications are."
Jamel Jaffer, an attorney for the American Civil Liberties Union (ACLU) and an observer of Khadr's trial, said the decision is a setback for U.S. government efforts to put some 380 other Guantanamo detainees on trial in military courts.
"The judge has said that the tribunal does not have the authority to try Omar Khadr," Jaffer said. "The grounds on which the court has made that decision are far-reaching and are going to have real consequences not only for Khadr, but for other prisoners who have been tried and may be tried in the future."
U.S. Marine Colonel Dwight Sullivan, the chief defense attorney representing Khadr, said the ruling reveals serious problems with the way U.S. military commissions were set up under the 2006 legislation.
"This indicates that the commission system cannot proceed -- that, once again, there's a fundamental impediment to the military commission proceeding," Sullivan said. "Once again, the military-commission system has demonstrated that it is a failure. Once again, we see a demonstration that we can't just set up another system of justice and call it 'justice.'"
Sullivan said the ruling also casts doubt on the legality of a guilty plea made in March by Australian detainee David Hick.
Hicks also was declared an "enemy combatant" rather than an "unlawful enemy combatant." After admitting to charges that he provided material support to terrorists, Hicks was sent from Guantanamo Bay to Australia to serve a nine-month sentence.
(RFE/RL's Kyrgyz Service contributed to this report from Bishkek. With material from agency reports)