A Moroccan man convicted of helping the September 11 hijackers commit mass murder appealed Tuesday against the maximum 15 year prison sentence imposed by a German court. Lawyers for Mounir el Motassadeq filed the appeal in Hamburg, court spokeswoman Sabine Westfalen said. It was unclear when the appeal might be heard in a federal appeals court. "Our only goal is to obtain an acquittal," defense attorney Udo Jacob said. The federal court convicted Motassadeq in November of being an accessory to the murder of the 246 passengers and crew on the four jetliners used in the 2001 attacks. A total of nearly 3,000 people died, many of them in the World Trade Center. A federal court in Hamburg on Monday gave Motassadeq the maximum penalty under German law of 15 years in prison.