By Nick Childs
BBC Pentagon correspondent
A tribunal set up by the Pentagon to review the status of detainees at Guantanamo Bay has ruled for the first time that a prisoner should be freed.
Almost 600 detainees are held at Guantanamo
The tribunals were set up after the US Supreme Court said prisoners could challenge their detention in court.
No details about the prisoner have been released, not even his nationality.
The man in charge of the tribunals, US Navy Secretary Gordon England, denied this was simply a case of an innocent bystander imprisoned by mistake.
He said it was more complicated than that.
But that may not be how the critics of US detainee policy will see it.
The Pentagon's review tribunals got under way at the end of July.
Thirty prisoners have so far completed the process.
The three-member tribunals have decided that 29 of them are indeed enemy combatants.
But now it has been decided that one is not.
It will not be the first time a prisoner has been released from Guantanamo.
More than 150 have been let go so far, or transferred to the control of their home countries.
But this will be the first release under this process.