There is a chilling element in Nehemiah's post in the words suggesting the family of Amy Bradley passed lie detector tests, and "then" the FBI proceeded with the investigation. Despite my criticism of the Ramseys for refusing interviews, I do not feel that way about avoiding polygraphs. No valid underlying medical basis has ever been established for the polygraph and the claims of accuracy are both inaccurate and self serving... and they tend to fail in ways that make innocent people look guilty and a confident criminal look innocent.
One example (sorry, there's math): Assume the polygraph is really 95% accurate as they claim. There's a thief in your company of a thousand employees. A guy you know is tested and fails. What is the probabiliy he is the thief? Answer: The probability is 1 in 50, not 95%. (The actual equation gives a slightly different result.) If the accuracy of the lie detector is in reality closer to 70%, the probability is 1 in 300. (There are similar calculations using Bayes' Theorem which show some shocking results for implications of false positives in hypothetical medical tests. There are "99% accurate" tests in which a positive result is virtually meaningless depending on how the 1% inaccuracy occurs.)
There are admittedly ways the polygraph can help solve a crime as a subjective tool but usually when the testee is guilty. The innocent person is at a statistical disadvantage when subjected.
