I didn't say that I thought you couldn't question a prisoner or suspect, simply that if he refused to answer your questions, you have no right to compel him to try to answer. Similarly, you have no right to mistreat the person in an attempt to extract information. Detaining a person does not give you a right to do whatever you want in the process of trying to get him to talk, it's really that simple.

Shortcut, you might want to hurt someone you thought might know something about your child, but if you did, you'd be just as much a criminal as the person responsible for hurting your child. A jury would have a harder time convicting you than a person who hurt a child, but you'd stand a good chance of being punished for your actions. You can't just go around hurting people whenever you feel justified. That's not how a society under the rule of law works, despite how much 24 you might have watched.