The promise of mind reading techniques whether it is a former FBI analyst or one of Paul Ekman's microexpression reading human lie detectors. I become aware of this cottage industry during every trial-by-media where suspicion piles upon someone not yet charged with murder.

I have to admit I am skeptical that anyone has such an amazing power to see through the facade of a stranger and with a greater-than-chance determine if they are telling the truth or not. Doubly so because I am someone who is constantly misinterpreted, I have to manage my gestures and facial expressions because my confusion is often misread as disagreement; my approval for disapproval; even a simple statement like "I'm not hungry right now" is wrongly generalized as not liking the particular cuisine... and not that I just don't want to eat anything right at this moment.

However if placed under the microscope by one of these former FBI body language experts would I feel a intense sense of validation ? Would I exclaim "yes, I feel seen, heard... you get me!"?

I have no  doubt some people are more perceptive about emotional nuances than others: film and theatre actors who are trained to observe and mimic, people who have grown up in abusive or emotionally unstable households and are hyper sensitive to small changes in the mood of others (which of course may make them prone to more 'false positives' and paranoia), and of course mentalists like cold readers and palmists. 

However being more emotionally perceptive doesn't necessarily mean you can tell if someone is lying - or a particular statement is false, especially if that person is especially good at telling the truth, or like me - their natural body language and expression doesn't express what you'd expect.

What I have greater faith in is that given even a small but emblematic example of a person's extemporaneous speech you could derive an accurate personality and world-view portrait of them. In the same way that an accent can help you pinpoint the geographical and economic origin of a person (think of comedies like The Nanny that play up on this convention). Harry Shearer once explained that to play Richard Nixon he channeled Jack Benny - believing that Nixon's persona and particularly his way of telling jokes was consciously or unconsciously modelled on that of Benny. Likewise Vladimir Putin's distinctive gait has been attributed to a prenatal stroke, or that his subordinates including Dmitry Medvedev have "copied the boss", the more persuasive explanation is that they all picked up the habit from watching Soviet Spy films as youngsters and wanting to emulate the hero. 

The kinds of films, television, and role models, books, music and lyrics that someone has absorbed would also influence or at least be indicative of their world view. Given enough of these tells, while I am not sure that you could tell if someone is or isn't a murderer, you could certainly gain a accurate insight into their worldview, the mental models they have about the world, what they value, what their ethics system is like etc. etc. 

How much information can you extract about a person from a written transcript that they aren't aware they are sharing is probably startling, but rarely or predictably "he's a murderer" level.