The polygraph would be used as the “bad cop” in the good cop, bad cop routine. After a line of questioning where the interrogator/polygrapher suspects lying, or

The polygraph would be used as the “bad cop” in the good cop, bad cop routine. After a line of questioning where the interrogator/polygrapher suspects lying, or is fishing for more information, they might say something like “everything sounded good but the machine is showing some deception. Is there anything you can think of that might be causing these readings? Anything you didn’t tell me? I want to get you out of here, but we need to resolve these results.” If the machine does show spikes during certain lines of questioning but not others, for instance about someone’s timeline on the day of a murder vs their relationship to the victim, it can be a reason to pursue further questioning in that area. Given all the ways polygraphs can be misused or abused, the only real use I see is as in interrogation tool. But given the issues with false confessions in general, I think the interrogation should hold less weight, but that is a whole other issue.