Can the state compel someone to reveal information that it suspects he has? If it can establish that this person has this information, and he refuses to provide it, could he not be punished for disobedience? And could continued non-compliance be answered with continued punishment? If torture is not just a means of compelling someone to reveal information, but a form of punishment, could it not then be justified?
But how would the state establish (beyond reasonable doubt?) that this person had the information? Would it not have to try him first, and then find him to be disobedient? Can someone be ordered to tell something that he knows, if this is for the safety of the public, or the "common good"?
The use of torture to establish that someone has information would not be justified since it is not punishment--this must be established by other means (witnesses and other evidence).
Already police officers can use pain and force to make someone who is resisting (actively or passively) comply with their orders, or at the very least to get them to stop resisting. Is this torture? Even though they do not have the authority to pass legal judgment upon them, it would seem that they can use force and inflict pain. Is this to be considered punishment? Or justified coercion?
There is also this point to be remembered: it is easier to verify that one is moving one's limbs (or not moving them) than it is to verify that someone is telling the truth, if he is the only one who knows whether what he is saying is true or not.