There is a federal law on this - The Polygraph Protection Act, if I recall correctly (it's been a while since I took a look at this) - and it does require employers to post a notice as to whether polygraphs will be administered but I don't believe it requires the results to be kept confidential.
I seriously doubt that an employer, even the police department, would release the contents to anyone. Even IF they asked you if you ever stole from your employer, you replied "no," and the results showed you lied, it's still not a wholly reliable test which is why polygraph results can't be submitted as evidence in court. There's no up side for the employer conducting the test to tell anyone else about the results.