A German appeals court has found a Moroccan, Mounir al-Motassadek, guilty of being an accessory to murder in the 11 September 2001 attacks on the USA.
Motassadek was previously cleared of knowing about the 9/11 plot
The Karlsruhe court sent the case back to a lower court for sentencing.
In August 2005, a Hamburg court jailed Motassadek for seven years, following a year-long retrial.
But the Karlsruhe judge on Thursday overturned the Hamburg court's decision to acquit Motassadek, 32, on thousands of counts of accessory to murder.
He now faces up to 15 years in jail.
Motassadek was originally jailed for 15 years in 2003, convicted of helping the 11 September plotters, who were based in Hamburg, with logistical support and other aid.
But that verdict was overturned by Germany's Supreme Court in 2004 and a retrial ordered.
The court ruled last August there was no proof that Motassadek knew about the 11 September plot and jailed him instead for membership of a terrorist organisation. He again appealed.
Defence lawyers at the retrial criticised the lack of direct testimony from witnesses held by the US.
The Moroccan acknowledges he was close to the hijackers but has always insisted he knew nothing of their plans.
He has admitted attending an al-Qaeda training camp in Afghanistan.