After four years of captivity, Khalid Sheikh Mohammed has confessed to being "
responsible for the 9/11 Operation, from A to Z". Waterboarding KSM was previously helpful in
revealing many details that we already knew about the plot that we'd already foiled.
There's a technique called "
cold reading" in which a mentalist watches their subjects' reactions and "picks up on signals from their subjects as to whether their guesses are in the right direction or not". A highly motivated cold reader can use their subject's own reactions, An interrogation subject is certainly highly motivated to discover what will elicit the most positive response from his interrogators, and after four years in detention he's certainly had a lot of practice learning what his interrogators do and don't want to hear.
This is one of several reasons why, if your goal is to obtain reliable actionable intelligence, you shouldn't attempt to obtain this information through torture. Because not only will this treatment produce a lot of intelligence that's not reliable, but because anything you do obtain will be highly suspect not to mention politically radioactive.