I don't put any stock into Debbie failing the poly. LE can tactically say what they want to further their investigation. They didn't even tell her how she failed it. It is a strategy. The reason they don't poly the dad is that they want a "failed" poly among the two of them to rip the seams open between them if there is anything one or both of them are hiding. They want finger pointing to start. They need to pit them against each other rather than with each other to ferret out truth if this is not a stranger abduction. If this is not a stranger abduction, my gut says dad is behind it and mom is not long off from realizing the truth. She seems of average intelligence, but likely with sub-par emotional intelligence. She may be in denial about her fiance and relationship. She seems genuine in her despair and lack of knowledge of what occurred. Police have NOT confirmed his alibi is solid, only he has. I am not banking that this was an inside "job" (that sounds awful), but if it was.. my 2 cents are on the father. He has little to say, his body language is guarded, he almost whispers his responses like he is withholding information, he doesn't seem to truly comfort her when she is melting down at moments, he seems detached, unemotional and flat. Sniffles, but no tears, no anger, no signs of distress other than guarded. JMO.