If you start using polygraphs, you might as well start using ducking stools to test for witches. To say that they "are not foolproof" is kind of understating things. They don't work reliably at all, and there is no scientific evidence to say that they do. You could just chuck dice.
Invactas: perhaps you can explain why the log for the emergency call records that the father said his daughter had gone berserk with a gun, or how the police came to be negotiating with someone inside the house whilst Bamber was outside with them?