Germany's top criminal court on Friday said it had refused to take up the appeal of a Moroccan man convicted of helping three of the Sept. 11 suicide pilots in their plot, leaving the 33-year-old with no further legal action possible in the country.

Mounir el Motassadeq was convicted in November of being an accessory to the murder of the 246 passengers and crew on the four jetliners used in the 2001 terrorist attacks.

He was sentenced to 15 years in prison, the maximum penalty possible under German law, and the Federal Court of Justice said it found el Motassadeq's appeal to be "unfounded" in a May 2 decision.

Germany's constitutional court in January had already refused to hear a separate appeal in which el Motassadeq's attorneys claimed that evidence from other terrorism suspects was not properly considered at his trial.

The decision Friday was a final step in what has been a long trip through the German legal system that began when el Motassadeq was arrested two months after the Sept. 11 attacks and has featured two full trials.

El Motassadeq's attorney Udo Jacob has said in the past that once he had exhausted appeals in Germany he would consider taking the case to the European Court for Human Rights.

El Motassadeq was first convicted and sentenced to the maximum 15 years in prison in 2003, but that verdict was overturned by a federal court the following year — largely because of lack of evidence from Al Qaeda suspects in U.S. custody.

At a retrial in 2005, the U.S. provided limited summaries from the interrogation of, among others, Ramzi Binalshibh, a suspected liaison between the Hamburg hijackers and Al Qaeda. The Hamburg court acquitted el Motassadeq of direct involvement in the attacks, but sentenced him to seven years for belonging to a terrorist group.

Prosecutors appealed the decision, and in November the Federal Court of Justice ruled that evidence showed el Motassadeq was aware Hamburg-based hijackers Mohamed Atta, Marwan al-Shehhi and Ziad Jarrah planned to hijack and crash planes, even though he might not have known the specifics of the plot. It convicted him of 246 counts of accessory to murder in addition to the membership in a terrorist organization charge.

Judge Klaus Tolksdorf ruled then that el Motassadeq had 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.