In a letter to the president yesterday, defence lawyers in the war crimes proceedings leading up to an expected trial for the 2001 attacks said the government was using secrecy to cover up torture after their clients were caught, held and interrogated.
They also accused the Obama administration of "suppressing evidence" and said the "self-serving" restrictions prevented them from properly making their case in legal proceedings against their clients, who face the death penalty if convicted of the attacks on US soil.
But defence lawyers said they lacked the necessary elements for a fair trial, and suggested it was too early to set a date.
"This process is completely unfair," said civilian lawyer James Harrington, who is representing Ramzi Binalshibh. "It's going to be a long time."
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In their letter, the 14 lawyers stressed that "the classification of the RDI (rendition, detention and interrogation) program is suppressing evidence, suppressing the truth, and ultimately will suppress any real justice," in violation of US law and of Washington's international obligations.
"These restrictions further violate our domestic commitment under the (United Nations) Convention Against Torture and the universal prohibition against silencing victims of torture."
The letter was signed by nine US military and five civilian lawyers paid by the Pentagon to defend the five men accused of plotting the hijackings that killed nearly 3,000 people in New York, Washington and Pennsylvania.
Following their detentions, in 2002 and 2003, the five suspects spent three years in secret Central Intelligence Agency prisons abroad where they were subjected to harsh interrogation techniques, including the simulated drowning technique known as waterboarding that is widely considered torture.