They did *not* take lie detector tests for the BPD. Or even the FBI. I'm not going to attempt to explain the DNA, as I have my own theory on that and we don't know enough about the mystery sample to conclude anything.
Did you work on this case?
You're wrong about the lie detector tests and a quick search into the documents of the case will show you that.
As for your theory about the DNA, you may want to check out this article that goes into detail about the DNA evidence and other evidence being looked at in the case.
http://www.cbsnews.com/stories/2004/12/16/48hours/main661569.shtml
What's interesting about this case is now investigators from the prosecutors office state on the records the Ramsey's were not involved in the murder. Now if there is any group of people who have full access to the evidence, including hold-back evidence it's them.