It is the first time the U.S. has held a closed session at the tribunals created to prosecute alleged terrorists at the base in Cuba.

Observers without security clearance were told to leave Thursday while a defense witness testified in the trial of former Osama bin Laden driver Salim Hamdan.

The defendant stayed in the courtroom.

The witness is Col. Morgan Banks, a psychologist with the U.S. Army Special Operations Command. Officials did not say why his testimony is being kept secret.
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