1.when answering questions a liar is not in a sentence mention own name ,FBI thinks if the suspect is always in the sentence omit me repeatedly ,so what he said it's questionable.
2.When people lie there will be a physical reaction ,this reaction would be to excess blood is flowing to the face ,cause nose to grow ,some people turn red .
3.statement of liar it's usually one shot , won't talk about it halfawy ，wait， i got it wrong,or let think about it such words.
4.The tone of lying there will be significant changes
5.On the liar's face a flash expression and this fleeting expression it's real .
6.repeatedly asking the same question ,can make liars show their flaws ,the purpose of FBI it's about letting the suspect from the state of lying break away from ,repeated questioning will only make him impatient,even angry ,or just to be honest.