I agree with this in principle, but for different reasoning.
Quite honestly, I simply believe that JR panicked when police asked him to grab a writing sample. Wasn't he asked to do so right by where the pads where kept? If he would have not grabbed those pads, it would have looked incredibly suspicious. He must have felt that police had already seen the pads sitting there, and didn't want to appear any more suspicious by not handing them over.
I completely disagree that JR didn't know anything beforehand. I will point to the fibers of his shirt that were found once more. Not to mention his suspicious behavior.
If he really didn't know anything until he found JBR, what would keep him from simply turning over PR -- if not that very day, eventually? "Keeping the family intact" doesn't really work as an excuse here, considering he could have kept BR. Are you supposing his love was so strong for PR that he wouldn't flip on her even after she killed one of his own children?
I believe that morning John was figuring things out. I think he was suspicious of the ransom note, but he was also likely aware of Burkes psychological problems. I think once he found the body that John became the world's first BDI, so no he couldn't just turn in Patsy.