A court acquitted a Moroccan on Thursday of helping the Sept. 11 hijackers while they lived and studied in Hamburg, citing a lack of evidence he was involved in the Al Qaeda cell's plans to attack the United States.

Abdelghani Mzoudi, a longtime acquaintance of lead hijacker Mohamed Atta (search) who even signed his will, smiled silently as he left the state court a free man after only the second trial anywhere of a Sept. 11 suspect.

The verdict infuriated victims' relatives and prompted Germany's chief federal prosecutor to criticize Washington for refusing to allow testimony from a U.S. captive -- Ramzi Binalshibh (search), believed to have been the hijackers' main contact with Al Qaeda. Even the presiding judge warned Mzoudi that his acquittal was "no reason for joy."

"You were acquitted not because the court is convinced of your innocence, but because the evidence was not enough to convict you," Judge Klaus Ruehle said in explaining the verdict. "In this case we have to give the defendant the benefit of the doubt."

The U.S. Justice Department issued a statement saying it regretted the acquittal and defending its level of cooperation.

"The United States has cooperated to the greatest extent possible in this and other terrorism prosecutions in Germany, consistent with security interests critical to the United States and the international community as a whole," spokesman Mark Corallo said. "Our cooperation with Germany will continue."

The U.S. trial of alleged Sept. 11 conspirator Zacarias Moussaoui (search) also has been denied access to Binalshibh and other Al Qaeda prisoners. Prosecutors there have argued that national security would be gravely harmed if details were revealed about the captives' sensitive interrogations.

Germany's top security official, Interior Minister Otto Schily, expressed support for the U.S. decision to withhold the documents even as he called the ruling "disappointing."

Mzoudi faced more than 3,000 counts of accessory to murder and charges of belonging to a terrorist organization allegedly led by Atta. Prosecutors said they would appeal the five-judge court's ruling, and chief federal prosecutor Kay Nehm said he was hopeful of winning a retrial.

Prosecutors alleged that Mzoudi provided logistical support to the Hamburg Al Qaeda cell, helping with financial transactions -- for instance, paying student fees -- and arranging housing for members to evade authorities' attention. He received training at a terrorist camp in Afghanistan in 2000.

But the case took a dramatic turn Dec. 11 when the court heard evidence that suggested Mzoudi had no knowledge of the Sept. 11 plot, prompting the court to order him freed from custody.

Prosecutors scrambled to salvage their case, producing new witnesses and evidence. In a last-ditch move, a lawyer for relatives of the victims sought to delay the verdict as Thursday's session began, asking the court to again seek evidence from Binalshibh. Ruehle rejected the request, then pronounced the verdict.

"We have no evidence that Mzoudi was aware of the planning," and his alleged help to the plotters "were everyday actions that he could have carried out without knowing anything about the attacks," Ruehle told the court.

Mzoudi, a slim, bearded man, left the court building alone through a side entrance clad in a gray coat and black cap. He refused to speak to reporters and his lawyers refused to say where he was going, but he was expected to remain under surveillance by German authorities. His lawyers said Mzoudi hoped to resume his electrical engineering studies in Hamburg.

Stephen Push, founder of the New York-based Families of Sept. 11 organization, whose wife was aboard the hijacked plane that crashed into the Pentagon, said the verdict left him "very upset."

Defense lawyer Michael Rosenthal called it a "great day for justice, which has showed its independence."

Ruehle said the court had struggled to establish the truth about Mzoudi's role, highlighting the fact that U.S. authorities refused to allow testimony from Binalshibh or access to transcripts of his interrogation.

Nehm said the U.S. stance hampered the trial.

"They must have their reasons, which they did not communicate to us," he said at his agency's headquarters in Karlsruhe. "Therefore I find this conduct by the United States incomprehensible."

"There will have to be a change of thinking in the United States, because clearly people there will now be asking why the German proceedings against Mzoudi ended this way," Nehm said.

A year ago, similar evidence in the same court secured the maximum 15-year prison sentence on the same charges against Mzoudi's friend, Mounir el Motassadeq -- the world's first Sept. 11 conviction. El Motassadeq's lawyers have seized on Binalshibh's absence and are demanding a retrial.

Experts said Thursday's verdict would not directly affect the pending appeal in el Motassadeq's case. But Kai Hirschmann, deputy head of the Essen-based Institute on Terrorism Research and Security Policy, said "it means that it will be very difficult in Germany to get trained Al Qaeda fighters behind bars."

Mzoudi was freed after the court received a statement that said the only people in Hamburg who knew of the plot were hijackers Atta, Marwan al-Shehhi and Ziad Jarrah as well as Binalshibh.

The judges -- who said the statement's unidentified source appeared to be Binalshibh -- decided they no longer had sufficient grounds to keep Mzoudi behind bars. They said there was no way to cross-examine the Yemeni so they had to take the statement at face value.

Hamburg's city government said it would examine whether it was possible to deport Mzoudi to Morocco, but conceded that it could not do so as long as any appeal is pending.