Berlin ? A Moroccan convicted of helping three of the Sept. 11 suicide pilots in their plot lost his final chance to appeal in Germany when the country’s top criminal court announced Friday that it had refused to hear his case.

Mounir el Motassadeq, 33, 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 in the U.S. He was sentenced to 15 years in prison, the maximum penalty possible under German law.

Germany’s Federal Court of Justice said in a short statement Friday that it had decided on May 2 that el Motassadeq’s appeal was “unfounded.”

“Therefore the verdict against the defendant el Motassadeq is legally binding,” the court said. It did not provide further details.

Even though all appeals are now exhausted, el Motassadeq’s attorney Udo Jacob said he would petition the original Hamburg court to reopen the case, which it is highly unlikely to do.