Im getting off tangent here as I was only disputing "torture doesnt work" but I'll answer your question. For the sake of this conversation, lets say it was the only method. Time is of an essence and you either torture the information out of him or people will die. What do you do?
EDIT: No, I wouldnt torture someone to protect child-rapists, who would? Not all pigs are created equally after all.
EDIT2: Ah, "potential" child-rapists. Well, thats just too abstract to answer clearly. Thought crime, so far, still isnt illegal so "potential" doesnt factor in.