As an investigator, I first try to assess how someone normally speaks. To do that, I begin an interview by asking questions that I know the answers to, like “What’s your full name?” or “Where do you live?” Some folks are naturally animated and talk fast; others are more subdued. Once I know which type of talker a person is, I start asking him questions that I don’t know the answer to. If his manner shifts abruptly—going from calm to agitated or lively to mellow—chances are he’s not telling the truth.
Gregg McCrary is a retired FBI criminal profiler and a crime analyst in Fredericksburg, Virginia.