An acquitted terror suspect refused to testify Wednesday at the retrial in Germany of a fellow Moroccan student accused of involvement in the planning of the Sept. 11, 2001 attacks. A lawyer for Abdelghani Mzoudi, whose not-guilty verdict was upheld in a federal court last week, said he would run the risk of being prosecuted again if he told the court what he knew about the defendant, Mounir el Motassadeq. Both Mzoudi and Motassadeq, friends of three Sept. 11 suicide hijackers who were based in the northern German port city of Hamburg, faced separate trials here for complicity in the attacks on the World Trade Center and the Pentagon which killed some 3,000 people. Motassadeq was convicted in February 2003 and sentenced to the maximum 15 years in prison. But the following year a federal court ordered a retrial, which is now underway here. Mzoudi was acquitted of the same charges -- membership in a terrorist organization and more than 3,000 counts of accessory to murder -- in October 2004. A federal court last week rejected an appeal from federal prosecutors for a new trial, citing a lack of evidence against him. The Hamburg court had hoped to gain more information from Mzoudi about Motassadeq's alleged role in the so-called Hamburg cell led by the hijackers' ringleader, Mohammed Atta. Mzoudi plans to return to Morocco in the coming days to head off a bid by authorities to deport him.