But in answer to that, you don’t have to prove POWs guilty of anything in order to hold them prisoner, just that they are in fact enemy combatants.
So at Guantanamo, we have three classes of people.
Enemy combatants who can be held indefinately without trial as long as conflict in Afghanistan goes on, but once the war is over you have to let them go and they can’t be charged with anything except war crimes (shooting at US soldiers isn’t a war crime). In my opinion most prisoners at Gitmo would fall into this category, I imagine Bush administration officials have a different view. These people aren’t guilty, but you don’t have to be “guilty” to be held.
Illegal combatants who can be charged with crimes. Murder, etc. You don’t get to shoot at US soldiers just because you don’t like them and they invaded your country, if you don’t fall into one of the categories quoted above you could be charged with murder for shooting a US soldier. However the problem is how are you going to prove it? In practice, it seems most would have to be treated as plain POWs.
People in the wrong place at the wrong time. Taliban soldiers move into a guys farm, US soldiers show up, firefight ensues, US soldiers capture everyone including the farmer, everyone gets sent to Gitmo including the farmer. But how is he going to convince the guards he wasn’t an irregular? It seems pretty difficult to do, especially if the actual irregular soldiers clam up. So this guy gets treated as a POW too, unless he can show somehow that he’s not.
So, you either get held (but not tried) as a POW, tried as a criminal, or let go as a noncombatant.
Note than in no case can you torture anyone, and in no case can you hold POWs or criminals incommunicado.
And one more thing. Nobody except an amatuer is going to be pulling off fingernails or the rack or rape or such. You don’t need any of that. Read the Gulag Archipelago, Soviet interrogators would have scorned such stuff and only amatuer guards or psychopaths would do such things. Hunger, cold, sleep deprivation, isolation, and psychological tricks are all you really need, as long as you have a few weeks or months to work with.