Hartmann faced repeated questions over the kind of evidence that will be used against Mohammed and his alleged co-conspirators. Evidence obtained through harsh interrogations are allowed under the commission system established by President Bush, which was later cemented into law by Congress.

But Wednesday, Hartmann would not say whether evidence obtained through waterboarding - which simulates the sensation of drowning - would be allowed at trial. CIA Director Michael Hayden acknowledged in Feburary that three detainees, including Mohammed, were subjected to waterboarding.

"The judge will make that determination," Hartmann said. "The US does not have a policy on that."