I used to think Patsy accidentally fractured JBR's skull but JBR was strangled an hour later, so how would that fit in? It doesn't. Patsy isn't going to strangle her child to cover up a fractured skull is she?
This is why I firmly believe BR was the culprit - for the head trauma AND the strangulation. It's the only scenario that can fit.
JBR and BR went downstairs, had some pineapple then went down to the basement. BR hit her with something, she fell and BR panicked, dragged her body across the hall to the cellar room, intending to hide her body. Then, for reasons of his own he strangled her fully.
That's when PR went down to find out what the kids were doing. She screamed and ran up to get John.
After panicked and lengthy discussions they decided to stage the scene to look as though an intruder had come into their home. It was the only way they could see to save BR from being taken from them.
They probably thought that once the time for the kidnappers telephone call had come and gone then the police would vacate their home and leave them in peace. They didn't think their home would be searched because their child had been 'taken', that's all.
Then....later they could discover their daughter's body in the cellar room. Hey! -the kidnapper had brought her body back. They killed her because the R's had gone against the strict instructions not to tell the police.
However....the plan went wrong because the police showed no signs of going. In the end JR had to 'discover' her body himself.