LE is more concerned with whether you agree or refuse to take their test, rather than the results - which are often inconclusive, and cannot be used in any proceedings against you. Now if you flat bomb it and show deception, they will follow you like a hungry dog after a meat wagon. Best advice is - never, ever take one unless it was arranged by your attorney. Then he or she can decide whether to share the results with LE.
Right. And there's been cases were people have passed lie detector tests and it meant nothing and it turned out they were the killer. (No links and I will say this is JMO as I've seen it happen when reading news articles, following other cases etc).