On Friday, September 4, at 8:30 pm EDT (check local listings), learn how Lt. Col. Stuart Couch, a government prosecutor set on convicting alleged 9/11 conspirator Mohamedou Ould Slahi, changed his mind after getting access to details of Slahi's treatment at the US prison in Guantanamo Bay. Couch, who was friends with a co-pilot of one of the jets hijacked on September 11, 2001, says Slahi was tortured.

    "I felt like what had been done to Slahi just reprehensible," Couch tells David Brancaccio. "For that reason alone, I refused to have any further participation in this case."

    In this web-exclusive video, Couch shares what he saw and heard at Guantanamo, and talks about his controversial decision.

    Also, on this week's NOW on PBS broadcast investigation:

    Is Obama tossing out the Constitution with his new anti-terror plan?

    Closing Guantanamo Bay's prison will do little to close the debate on what we should do with alleged terrorists. On Friday, September 4, at 8:30 pm EDT (check local listings), NOW, as part of a collaboration with the nonprofit investigative unit ProPublica, investigates the controversial tactic of "preventative detention," a government plan that may detain suspects indefinitely without trial or even formal charges. Implementing such a plan may have far-reaching consequences on not just our fight against terrorism, but the integrity of the US Constitution and the cause of human rights.

    Even with President Obama in office and Guantanamo's days numbered, we're still asking: What price will we pay for peace on the ground and peace of mind? This time on NOW.