A German federal appeals court on Thursday convicted a Moroccan friend of three of the Sept. 11 homicide pilots as an accessory to murder in the attacks, ruling that evidence showed he played a direct role in the plot.

The Federal Court of Justice found that a Hamburg court decided wrongly last year to acquit Mounir el Motassadeq of direct involvement in the attacks, even though it convicted him of membership in a terrorist organization and sentenced him to seven years in prison.

It ordered the Hamburg court to reconsider his sentence. El Motassadeq could now face a maximum 15 years in prison.

"The defendant is guilty not only of membership in a terrorist organization, but also as an accessory to murder of the 246 passengers and crew members of the crashed aircraft," the federal court said in its ruling.

El Motassadeq was a close friend of hijackers Mohamed Atta, Marwan al-Shehhi and Ziad Jarrah when they lived and studied in the northern port city of Hamburg.

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In his ruling, Presiding Judge Klaus Tolksdorf said the evidence showed el Motassadeq knew they planned to hijack and crash planes, and said it was irrelevant to his guilt whether he knew of the planned timing, dimension or targets of the attacks.

Tolksdorf said the evidence showed that el Motassadeq, 32, helped "watch the attackers' backs and conceal them" by doing things such as helping them keep up the appearance of being regular university students — paying tuition and rent fees and transferring money.

"He made easier and helped the conducting of these attacks," the judge said.

"We won, I'm ecstatic," Dominic Puopolo Jr., an American co-plaintiff whose mother died in one of the planes that struck the World Trade Center, told The Associated Press by phone from South Beach, Florida.

"This man's actions as a coconspirator caused thousands upon thousands of families untold grief, and to know that the German justice system has worked — it's a tremendously special day," he added. "I'm very glad the appeals court saw through what I believe to be a lot of smoke and mirrors."

El Motassadeq has been free during his appeals process. Prosecutor Gerhard Altvater said his office would now consider asking for an order that he be taken back into custody as the lower court considers his sentencing.

It was unclear when the Hamburg court would take up the case. The new hearing is expected to last only a few days.

Defense attorney Ladislav Anisic said that, once sentencing is complete, he might appeal el Motassadeq's case to Germany's highest court, the Federal Constitutional Court.

El Motassadeq was convicted of membership in a terrorist organization and thousands of counts of accessory to murder in 2003 — becoming the first person convicted anywhere on Sept. 11-related charges. He was sentenced to the maximum 15 years in prison.

However, the federal court overturned that verdict in 2004, largely because of a lack of evidence from Al Qaeda suspects in U.S. custody, and sent the case back to a Hamburg court.

After a retrial, el Motassadeq was again convicted last year of membership in a terrorist organization that included Atta and the two other suicide pilots who had lived in Hamburg — al-Shehhi and Jarrah.

But he was acquitted of being an accessory to murder, after the court ruled it did not have enough evidence that he knew of the hijackers' plot and thus could not convict him of charges based on being directly involved in the Sept. 11 attacks.

El Motassadeq was sentenced to seven years in prison but was freed from custody in February pending the outcome of his appeal.

Defense attorneys had appealed, asking for a new trial to try and win el Motassadeq's acquittal, while prosecutors had argued for a tougher sentence and the conviction on charges of being directly involved in the Sept. 11 plot.

Tolksdorf said he found that the defense argument was "clearly unfounded."

At the retrial, Washington again declined to allow testimony by Ramzi Binalshibh, the Hamburg cell's suspected liaison with Al Qaeda now being held by the U.S. at Guantanamo Bay, Cuba, and provided only limited summaries of his interrogation, which the Hamburg court said had no value as evidence. However, Tolksdorf said the Hamburg judges had taken sufficient account of that.

The Moroccan admitted training at an Al Qaeda camp in Afghanistan and acknowledges he was close to the hijackers, but insists he knew nothing of their plans. He has spent a total of about three years in jail during the proceedings.

Hamburg authorities have said that, once legal proceedings against el Motassadeq are over and his sentence served, they will deport him to his native Morocco.