Hmmm ... still thinking about the garotte ... If JB was struck by the flashlight while still in the kitchen, and then BR tried to get her down to the basement to hide her until she would "wake up", how would he do that when he most likely could not lift and carry her? He might have tried to drag her by the back collar of her night-dress, which then could have caused the triangle-shaped bruise on the front of her neck. What if he then thought he had a better idea and made the "garotte" only intending to use it to be better able to drag JB to the WC area? The knot around her neck so it wouldn't slide off, and the handle to provide a better purchase for his hands when pulling her body so the cord would not keep sliding through his fingers?
My point is, maybe the garotte was not intended at all to be a "garotte" and was only made to help BR drag JB to some place out of sight in case his parents got up. Then he went and got one of her blankets and put over her, either to further hide her or keep her warm.
The reason that a child the age of 9 can't be charged with murder in CO (and elsewhere, or other young aged children), is because they can't form an "intent" to murder. That doesn't mean that some of them actually can't form such an intent. But in general, a child that age might strike a killing blow in the heat of the moment without meaning to kill but only as an expression of angry retaliation. If that's what happened in this case, then BR may have been startled when she fell and just lay there -- this had not happened before when he'd hit her. He may not have realized "Well, she's unconscious" because it was just outside his experience. So he may have expected her to "wake up" after a little while, and not even realized he was strangling her while dragging her any distance with the "garotte".
Just thoughts.