* Military investigator says suspect was free to leave
* His statement to investigators remains top secret
An FBI agent and a U.S. military investigator testified on Monday that a Saudi prisoner accused in the Sept. 11 plot had freely and voluntarily answered their questions during an interrogation at the Guantanamo Bay U.S. Naval Base in 2007.
But at the pretrial hearing, a defense attorney for the prisoner, Mustafa al Hawsawi, questioned how voluntary those statements could have been after 4-1/2 years in CIA and U.S. military custody.
The investigators said Hawsawi had not been advised of his right to remain silent, was not allowed to consult a lawyer and was not told that his words could be used against him.
He was told that it was entirely up to him whether to continue with the questioning that took place over four days at the naval base in Cuba, they testified.
"He could stop the conversation at any time," said Stephen McClain, an investigator with the military's Criminal Investigative Task Force. "He could leave the room at any time."
Was he "free to get up and get on a plane and go home?" asked Hawsawi's defense attorney, Navy Lieutenant Commander Walter Ruiz.
McClain acknowledged that he was not.
Hawsawi is an alleged al Qaeda financier accused of providing money, credit cards and Western clothing to the hijackers who commandeered four commercial planes and crashed them into the World Trade Center, the Pentagon and Pennsylvania field on Sept. 11, 2001, killing nearly 3,000 people.
He was captured in Pakistan in March 2003 and held by the CIA in a series of secret prisons, where he claims to have been tortured during interrogations.
He and four co-defendants were transferred in 2006 to Guantanamo, where they are facing conspiracy, murder and other charges in a U.S. war crimes tribunal that could end with their execution.
Prosecutors want to start the trial in September 2014 but defense attorneys say it could take them three more years or longer to prepare their case.
Any statements that may have been obtained from them via torture or coercion cannot be used as evidence in their trial.
McClain and FBI Special Agent James Fitzgerald were part of a "clean team" that questioned Hawsawi and other prisoners at Guantanamo to prepare the charges.
They said Hawsawi had been "friendly but reserved," during the sessions, which were regularly recessed so he could eat, sleep, pray and use the bathroom.
Ruiz has asked the judge, Army Colonel James Pohl, to dismiss the charges against Hawsawi because no interpreter was present when the native speaker of Arabic was questioned in English.
The investigators said Hawsawi spoke English proficiently and seemed to understand them fully.
Hawsawi's statements to the investigators remain classified as top secret.
Ruiz said he had been given a very heavily redacted copy and held up several pages in the courtroom. "They're black pieces of paper," the judge said.
Prosecutors will not give Ruiz and the other defense lawyers unredacted copies of the classified evidence until they sign an agreement promising to safeguard it.
Ruiz and most of the other defense lawyers have refused to do that until the judge resolves their requests for changes and clarifications.
That topic is expected to take up much of the weeklong pretrial hearing that began on Monday at the remote naval base in eastern Cuba.