Thank you for sharing your fiancé's experience. It is a mistake for anyone accused of a crime to submit to any polygraph "test." Law enforcement agencies use the polygraph as a ruse to get suspected criminals to agree to be interrogated without a lawyer. The examinee's "failing" may be part of the interrogation plan.

I would be happy to review the recording of your fiancé's polygraph interrogation along with the polygraph data and provide a written critique that might be useful in a pretrial motion. In a recent New Mexico case, post-polygraph statements made by a defendant were ruled inadmissible owing to questions about their voluntariness:

https://antipolygraph.org/blog/2016/06/26/federal-judge-throws-out-fbi-post-polygraph-confession-over-concerns-about-voluntariness/

Some of the pleadings, facts, and arguments from that case may be of interest to your fiancé's lawyer. They are available here:

https://antipolygraph.org/litigation.shtml#tennison

My contact details are in my signature block below.