Let's use me as a very realistic example. If I am being tortured, all I need to know is what they want me to say .... and that's what I will tell them. I don't think my "forced confession" is going to save anyone's life - probably be the cause of someone's death...
First, you yourself would not make a very good interrogator, so make sure you don't quit your other day job.
Second, when you interrogate, you first isolate, then you deprive, then you ask for details.
You do not lead the witness (so to speak).
Thus the subject of the interrogation is forced to cough up facts, not lies.
Third, you continue the process over and over under extreme stress so that the subject's mind can only recall the truth not the lies.
Fourth, your transcribers cross reference the subjects statements and you continue to interrogate until you have ferretted out all the lies.
Those are things you yourself simply know nothing about.