Is culpability relevant to torture's permissibility?

Thanks to Chris Eberle for his thoughtful comment on my question about evaluating the moral permissibility of torture based on the fruits of torture.  I need to think more about this, but let me offer a couple off-the-cuff reactions: First, if KSM's culpability for the harm that the torture is designed to prevent is relevant to our moral evaluation of the torture, this seems to blur the line between punishment and interrogation.  Given the due process protections that we've built around the state's punishment function, but that are not (for good prudential reasons) always present in the interrogation function, blurring those lines gives me pause.  Second, if KSM's culpability, as opposed to mere knowledge, is discovered or confirmed through torture, I am not sure why that culpability is relevant to the moral evaluation.  Just as we have to judge the morality of the Iraq invasion based on the evidence presented to President Bush at the time -- not the evidence (or lack thereof) presented after the fact -- don't we need to evaluate the moral permissiblity of waterboarding KSM based on the government's knowledge at the time it decided to waterboard him?

That said, there is something intuitively appealing about Chris's assertion.  Suppose that in one holding cell is a waiter who served dinner to KSM and his colleagues while they openly discussed where they had hidden the nuclear device.  The waiter refuses to recount what he heard, citing his personal belief in a waiter-customer confidentiality rule.  In the other holding cell is KSM himself, and he's chanting "I hid a nuclear device and I won't tell you where!"  Are more coercive interrogation techniques morally permissible for KSM than for the waiter?  Perhaps they would be if we are willing to use interrogation as punishment, but in that case the punishment should not be up to the ad hoc conclusions of the interrogators, should it?  At a minimum, torture would not be morally justified for KSM or the waiter.  Waterboarding -- being designed to inflict severe physical and mental suffering based on the intentional creation of the perception of imminent death by drowning -- is torture.