The problem is the old "what if"?

What if you have captured someone who admits having kidnapped a child and imprisoned her in a small airtight hidden chamber and is saying "The child will now die. She will die if I stay here, and since I cannot trust you to ignore my crimes, I will take my revenge on the world by letting her die even if you release me now. And no, I will not tell you where she is, purely to prevent you rescuing her".

Do you then use torture to extract the information of where the child is, or do you leave the child to die?

And if you will use torture then, what if you are sure, but the captive does not admit?

How sure do you have to be?