JohnFear, you trust Nancy's mom. I hope you extend the same courtesy to her father too.
The Rentz family believes (I'd say they know but I'm assuming) that the murderer of their daughter is Brad.
No grieving parent wants to have to believe, let alone face, the horrid thought that their son-in-law murdered their daughter. One would imagine they would hope it WAS someone else, because the pain increases exponentially that someone you trusted and loved took the life of your precious child.
And yet they believe/know. Think they might know something we, the general public, don't yet know, that hasn't been testified to yet? I'd say yes.
You said you trust Nancy's mom, Donna. Donna knows Brad killed Nancy. Trust THAT!
She believes it, but she doesn't know it. The only people that know it are Brad Cooper, and/or the person that did it if it wasn't Brad Cooper.