Mohammed and four co-defendants were arraigned Saturday in Guantanamo Bay, Cuba.
Attorney David Nevin said new rules imposed by the U.S. government prevent him from talking to his client about alleged mistreatment by U.S. authorities after his arrest in connection with the Sept. 11, 2001, terrorist attacks, the Los Angeles Times reported Monday.
Mohammed is charged with murder, terrorism and conspiracy, the report said.
"We are operating under a regime here," Nevin said. "We are forbidden from talking to our clients about very important matters.
Nevin says the government wants Mohammed executed. "They want to extinguish the last eyewitness so he can never talk about his torture. They want the political cover so he'll be convicted and executed," he said.
Government documents show Mohammed was subjected to waterboarding at a classified CIA "black site" before he was moved to the prison at Guantanamo Bay.
Army Brig. Gen. Mark Martins, the chief prosecutor at the military trial, said defense lawyers could talk to their clients but could not show them classified documents that disclosed harsh treatment.
Martins said talk of the death penalty is premature, the newspaper reported.
Exploding whale video goes viral on Internet
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'