The U.S. initiative came at the start of the retrial of Mounir el Motassadeq, a 30-year-old Moroccan charged with aiding the three Hamburg-based suicide hijackers. He denies the charges.
Replying to the Hamburg state court's request for testimony by key al Qaeda operatives in U.S. custody, the State Department said the United States would provide unclassified summaries, apparently of interrogations.
"This is a bit of progress," trial judge Ernst-Rainer Schudt said in court.
El Motassadeq won a new trial in March after a German appeals court ruled his first one unfair because the U.S.-held witnesses did not testify. He remains charged with more than 3,000 counts of accessory to murder and membership in a terrorist organization.
Now, the quest for testimony from the witnesses — Ramzi Binalshibh and Khalid Shaikh Mohammed — is critical to Germany's second attempt to convict him.
Binalshibh, a Yemeni, is believed to have been the Hamburg cell's key contact with Osama bin Laden's al Qaeda organization. Mohammed is thought to be the mastermind of the Sept. 11 attacks.
Testimony in person would not be possible, the U.S. letter said. But in el Motassadeq's first trial, the U.S. Justice Department refused to allow even transcripts of interrogations to be admitted as evidence.
El Motassadeq denies the charges. He has been free since the Hamburg court ordered his release in April pending the retrial.
"At no point did he have any knowledge prior of the plan prior to the attacks," defense lawyer Udo Jacob said in court Tuesday.
In his opening challenge, defense lawyer Josef Graessle-Muenscher demanded the court throw out the case. The judge did not immediately rule on the motion.
The lawyer argued that even the newly promised evidence would be inadmissible because it would be tainted by suspicions that al Qaeda and Taliban prisoners were tortured in U.S. custody.
The court's judgment "must not be the result of torture and humiliation, and it must not reward wrongdoing by a government," Graessle-Muenscher told the court.
He cited reports from prisoners released from U.S. military detention at Guantanamo Bay, Cuba, and the policy of holding Taliban and al Qaeda suspects without giving them the usual rights of prisoners of war set out in the Geneva Conventions.
After two failed attempts by Germany to convict alleged Sept. 11 coconspirators, Judge Schudt said the Hamburg state court wouldn't be swayed by political pressure.
"For me, this is not about fulfilling the expectations of governments or the public," he said.
El Motassadeq smiled but said nothing as he entered the court Tuesday. In court, he briefly answered questions about his identity but turned down the judge's offer to respond to the indictment.
El Motassadeq is accused of helping pay tuition and other bills for members of the Hamburg al Qaeda cell, which included suicide hijackers Mohamed Atta, Marwan al-Shehhi, and Ziad Jarrah, to allow them to live as students as they plotted the attacks.
He admitted training in bin Laden's camps in Afghanistan, and witnesses at his first trial testified that he was as radical as the rest of the group, often talking of jihad — holy war — and his hatred of Israel and the United States.
He signed Atta's will and had power of attorney over al-Shehhi's bank account.
El Motassadeq has said he was nothing more than close friends with the others and did only things that a good Muslim would do for any "brother."
Lack of testimony from Binalshibh or Mohammed also played a large role in the February acquittal in the same court of el Motassadeq's friend and fellow Moroccan Abdelghani Mzoudi, who faced identical charges.
"We have made it clear to the United States that we depend on being able to hear Ramzi Binalshibh and Khalid Shaikh Mohammed as witnesses," German chief federal prosecutor Kay Nehm was quoted as saying in this week's Focus magazine.
Trial dates are scheduled into January, but more can be added if needed.