The first person convicted in the Sept. 11 plot appealed the verdict, arguing the court did not hear testimony from another suspect in U.S. custody, his lawyers said Thursday.

Mounir el Motassadeq, 28, was found guilty Wednesday of belonging to a terrorist organization and 3,066 counts of accessory to murder for helping with rent, tuition and other payments that let members of the Hamburg-based Al Qaeda cell keep up the appearance of being normal students.

El Motassadeq, a Moroccan, was sentenced to the maximum sentence allowed under German law -- 15 years.

Lawyer Hans Leistritz said the main basis for his appeal, filed late Wednesday, was that the court was denied the opportunity to hear testimony from Ramzi Binalshibh, a Yemeni suspected of being the Hamburg cell's main contact person with the Al Qaeda network.

Binalshibh was arrested in Pakistan on the anniversary of the Sept. 11 attacks and is now in U.S. custody.

The court could not get him released to testify, and the German government refused to turn over their files on him, saying transcripts of interrogations provided by the United States had been provided to them for intelligence purposes only.

The defense had the same problems getting testimony from Mohammed Haydar Zammar, a Syrian-born German in Syrian custody who is suspected of being a Hamburg Al Qaeda recruiter.

But Hamburg University law professor Stefan Oeter said he did not think an appeal would succeed because the five-judge panel had made a concerted effort to get the testimony of both men.

"If the executive has done its best to get formal testimony from these two people, I think that's enough and it's not cause for appeal," Oeter said.

If the verdict stands, experts say it will set a precedent that could help convict other suspects, including one already in custody.

"[El Motassadeq] was not the one who directly carried out or planned these attacks, but he was a supporter who assisted in carrying out a terrorist attack and what happened [with the verdict] made it much easier for German courts to get these people behind bars," said Kai Hirschmann, a terrorism researcher at the Federal College for Security Studies in Bonn.

Abdelghani Mzoudi was picked up in October on the lesser charge of supporting a terrorist organization.

Formal charges are expected in the next few months and the trial should get under way before the end of the year in the same court that convicted el Motassadeq.

Germany has also issued international arrest warrants for Said Bahaji and Zakariya Essabar as suspected Hamburg cell logisticians, and authorities are still investigating others with links to the group. Bahaji and Essabar disappeared from Hamburg before the attacks.