Lawyers for 11 September suspect Abdelghani Mzoudi have asked a German court to acquit him saying he knew nothing of the attack plans.
Mr Mzoudi, 31, is accused of being an accessory to the murder of more than 3,000 people in the US attacks, and being a member of a terrorist group.
Last month, a judge released him from custody in the light of new evidence that could exonerate him.
Prosecutors say Mr Mzoudi helped the cell responsible for the attacks.
They want him to be given the maximum sentence of 15 years in jail.
In closing arguments on Thursday, Mr Mzoudi's defence lawyer Guel Pinar said her client knew cell members but was not part of the plan to attack the United States.
"Abdelghani Mzoudi belonged to the group of students around Mohamed Atta. He spent time in Afghanistan," she said. "The evidence shows that - but no more than that."
Truth
New evidence that led to Mr Mzoudi being released from court in December came in the form of a statement from an unidentified informant saying that there were only four people in the Hamburg cell responsible for the attacks - three pilots and Ramzi Binalshibh who is already in US detention.
The source was not named but the court said it believed it was Mr Binalshibh.
Ms Pinar said the US Justice Department has refused the Hamburg court access to Mr Binalshibh and his interrogation statements.
"The American government has hindered rather than helped the court in its search for the truth," she said.
Prosecutors have called for Mr Mzoudi to be jailed for 15 years as they insists there were "sufficient indications available to determine his involvement" in the attacks.
A verdict is expected later this month.
Convicted
Mr Mzoudi is the second person anywhere in the world to be tried over the attacks.
Moroccan Mounir al-Motassadek was jailed in Germany in February as an accessory to more than 3,000 murders in New York and Washington as a result of 11 September.
The court which convicted Motassadek heard that he was a member of the Hamburg cell which planned the terror attacks.
He was jailed for 15 years.
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