These terrorists captured are enemy combatants. They are not subject to US law, they are subject to military tribunal. Gitmo is a military detention center.
The only thing they've been subject to so far is indefinite detention without trial. Why anyone trusts the gov't in this is beyond me? If they are guilty, try them and sentence them. It really is that easy.
America as a whole has a rich history of freedom and human rights. Have we had our missteps? Absolutely. They typically have occur during some kind of war.