Lawyers said the proceeding had been compromised by a U.S. refusal to provide access to the key witness.
Defense attorneys for Mounir Motassadeq, a Moroccan citizen, had repeatedly asked for testimony from Ramzi Binalshibh, who is in secret U.S. custody. U.S. officials have called Binalshibh a central conspirator in the attacks but declined to produce him for the trial, citing national security concerns.
The appeals decision Thursday was a new setback for German prosecutors as they try to convict what they have said are remnants of an al Qaeda cell that was based in the port city of Hamburg. One month ago, a court there acquitted another Moroccan, Abdelghani Mzoudi, on charges of aiding the hijackers. In that case, the chief judge also cited the lack of access to witnesses being held by the United States.
The appeals court found Thursday that the Hamburg court that convicted Motassadeq had not adequately considered the implications of the absence of evidence from Binalshibh.
The appeals court concluded that it “will not make any decision whether the United States has the right to withhold the witness or not,” an attorney for Motassadeq, Josef Graessle-Muenscher, said after the ruling. “If the United States does not deliver the witness, they have to bear the consequences.”
Motassadeq, a former engineering student from a prominent Moroccan family, was convicted in February 2003 of membership in a terrorist organization and 3,066 counts of accessory to murder, a figure intended to match the death toll in the suicide attacks in New York and on the Pentagon.
A panel of judges found Motassadeq guilty on the basis of evidence that he had a long association with the hijackers and knowingly helped them stage the attacks through such actions as transferring money. His defense acknowledged that he knew the men but said he had no knowledge of their plans and helped them out of obligation to fellow Muslims.
Motassadeq was given a sentence of 15 years, the maximum allowable under German law. The country has no death penalty.
Prosecutors had presented similar evidence at Mzoudi’s trial last year, but in December their case was compromised when a German police agency disclosed unconfirmed intelligence indicating that only four people, Mzoudi and Motassadeq not among them, knew the hijackers’ plans.