He was the first person ever convicted for complicity in the attacks on the World Trade Center and the Pentagon.

The Moroccan was put on a plane at Frankfurt airport and sent back to his country of origin, according to an airport police spokesman, speaking to the German national news agency DPA.

Several police officers accompanied him.

Earlier he had been taken by helicopter from the Hamburg jail where he has been serving his prison term to Frankfurt, according to Spiegel Online and Bild daily.

Photographs carried by DPA showed him dressed in a checked shirt and beige trousers, being led blindfolded and handcuffed by two police officers to a waiting chopper.

Motassadeq, who was held in prison just after his arrest in late 2001, had served nearly all of his sentence.

He has admitted to having links to the hijackers, but he maintained his innocence in a five-year court battle.

The Moroccan was friends with members of a Hamburg-based cell including their leader Mohammed Atta. He helped to cover up their whereabouts while they were taking flying lessons in the United States and handled a bank transfer for them.