3. Never let them know that you are onto something
Never in any situation fall weak and confess that you are interrogating a particular case where the person (standing right in front of you) has been considered as a suspect. This obligation to confess may happen when the liar in question is a friendly colleague who you may know for quite some time.
While interrogation, avoid asking questions like “Is something bothering you?” or “Are you okay?”, because if you do chances are the liar will get to know that you are onto something. Once a liar who had criminal or deceiving intentions get alert, it may become tougher to get the truth out of him.