Karlsruhe, Germany ? A Moroccan man was convicted of being an accessory to murder in the Sept. 11, 2001, attacks, as a German appeals court ruled Thursday that evidence showed he knew the plotters planned to hijack and crash planes.

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 as it convicted him of membership in a terrorist organization and sentenced him to seven years in prison.

El Motassadeq, 32, was a close friend of hijackers Mohamed Atta, Marwan al-Shehhi and Ziad Jarrah when they lived and studied in Hamburg. He has acknowledged training at an al-Qaida camp in Afghanistan but insists he knew nothing of their plans.

“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.

It ordered the Hamburg court to reconsider his sentence. El Motassadeq, who was not present for the ruling, now could face a maximum of 15 years in prison.

That could end a five-year saga, which started with his arrest in November 2001 in Hamburg and has featured two trials – although defense lawyers held out hope of taking his case on to Germany’s highest court.

El Motassadeq, who already has spent a total of about three years in prison, has been free since February, although he has had to hand in his passport to authorities and report regularly to police.

No date was set for sentencing, and federal prosecutors said a Hamburg court later Thursday rejected their plea to return him to prison immediately. Prosecutors said they would appeal that decision.

In his ruling, federal court presiding Judge Klaus Tolksdorf said evidence showed that el Motassadeq 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.

Tolksdorf said it was irrelevant to el Motassadeq’s guilt whether he knew of the planned timing, dimension or targets of the attacks.

Dominic Puopolo Jr., an American co-plaintiff whose mother died in one of the planes that struck the World Trade Center, said by phone from South Beach, Fla. that he was “overwhelmed with joy.”

“This man’s actions : caused thousands upon thousands of families untold grief, and to know that the German justice system has worked – it’s a tremendously special day,” Puopolo said.

German prosecutors, who have seen several setbacks during recent years in their pursuit of associates of the 9/11 hijackers, also hailed the verdict.

“Beyond this case, I can see now that the state of law has sufficient ability to deal with such extraordinary crimes,” prosecutor Gerhard Altvater said.

A lawyer for el Motassadeq pledged that “the defense will continue to pursue its efforts to secure an acquittal.”