US defence lawyers queried today the credibility of Guantanamo military tribunals.
A civilian appeals court has now reversed the verdicts of the only two Guantanamo prisoners convicted in trials by tribunal, casting a long shadow over legal proceedings at the US concentration camp.
A federal appeals court threw out the conviction of Ali Hamza al-Bahlul last Friday, who was charged with providing material support to terrorism and conspiracy.
That followed the dismissal in October of the conviction of Salim Hamdan, a driver for Osama bin Laden.
In both cases, the reasoning was the same.
The court determined that before the Military Commissions Act of 2006, which authorised the tribunals for terrorism suspects at Guantanamo, only violations of the international law of war and pre-existing federal offences were subject to trial by military commission.
The court said the charges of material support for terrorism and conspiracy did not meet that standard.
They were the only prisoners convicted in trial by military commission. The five other convictions of Guantanamo prisoners all came through plea bargains.
"The fact that no conviction can stand up on appeal does not bode well for the system," said James Connell, a lawyer for Ammar al-Baluchi, who is one of the five charged in the September 11 attacks.
Human Rights Watch lawyer Andrea Prasow said it revealed "just how shaky the entire system is."
She said: "Men's lives are on the line. I think that's all the more reason for the government to proceed very cautiously and make sure that it is confident it has a firm legal basis upon which to pursue these charges."