Basically this.  Confronting people with their own lies is a surefire way to pry the truth out of them.  People can lie about the truth, and deny the truth... but people can't lie about a lie.  It's some crazy psychological thing with humans.  If someone is lying, and you confront their lie and ask if it's true, they will never say yes.  They will avoid answering and say things like "well you believe what you want to believe" and stuff like that.  Learned that from listening to a guy who is a professional deception detector.  He says even with knowing the things he does, he can't even utilise what he knows to be 100% deceptive himself.