See he Difference

One examiner who had been a police officer was captured on a hidden camera saying that he could usually tell within five minutes of meeting a suspect whether or not that suspect was guilty. This is the ultimate in polygrapher arrogance. If the examiner can really make that distinction almost immediately after meeting someone, why does he need the machine?

This is not to say that civilian polygraphers do not make determinations of guilt before the test has even been run ー they do. It's human nature.