There is no concrete evidence that someone in the house did it is true for sure. And that being said, Their first time committing a horrible murder and they leave no real evidence behind showing it was them and only them?? That does not strike anyone as odd? All the convoluted things in this case and not one thing points to someone in that house, and says it is them??
With that being said, an intruder:
-Breaks into the home
-Writes a ransom note with materials from the house
-Sexually assaults JB
-Murder's her
-Leaves
and leaves no real evidence behind, doesn't wake anyone up?