[cafard]

William Casey, who was Reagan's first CIA director, told journalists that passing polygraphs is an easily learned skill. Some may not need the training: if there is no psychological stress involved in lying, why should there be physical symptoms?

[vidarh]

Which is still irrelevant here. The willingness - or not - to take the test acts as a filter. Beyond that, a case review is carried out. If the case review finds they have sufficient evidence, the test does not matter. If the case review finds they have insufficient evidence, then you should not have been charged in the first place.