Psychopaths often pass lie detector tests with flying colors.
Are you saying that lie-detectors can be used only on those who tell the truth?
Don't make much sense to me.
There is one kind of test that never fails. And I have the feeling that you may like it.
In the good old days a woman accused of witchcraft was tested in the following way: she was tied up and dunked in deep waters - if she floated, she was guilty of being a witch; if she drowned, she was innocent.