A civilian appeals court has now reversed the verdicts of the only two Guantanamo Bay prisoners convicted in trials by military tribunal, casting a shadow over proceedings set to resume this week at the U.S. base in Cuba for the men accused in the Sept. 11 terrorist attack.

A federal appeals court on Friday threw out the military commission conviction of Ali Hamza al-Bahlul, who was charged with providing material support to terrorism and conspiracy for making propaganda videos for al-Qaida. That followed the dismissal in October of the conviction of Salim Hamdan, a driver for Osama bin Laden.

Al-Bahlul and Hamdan were the only prisoners convicted in a trial by the tribunals known as a military commission. The five other convictions of Guantanamo prisoners came through plea bargains.

There are two pending death penalty cases at Guantanamo: one against a prisoner accused of orchestrating the attack on the USS Cole in 2000, the other against five men accused of planning and aiding the Sept. 11 terrorist attacks. But the recent reversals have raised new questions about the use of military commissions in complex terrorism cases.