akh, I totally agree with you. As you point out, if BR was only responsible for the head wound, then it doesn't make sense to me that the parents would cover this up with such an elaborate "kidnapping by a crazed sicko gone wrong" scheme. It is much more plausible that they would have immediately called 911. And remember, the head wound wasn't immediately apparent to anyone -- even the coroner didn't know about it until the autopsy was conducted and they found the horrible skull fracture. So unless the parents actually witnessed BR hitting JBR over the head, they wouldn't even know this wound was there.
What makes more sense to me is exactly what akh theorizes -- I think BR not only hit her over the head, but also strangled her. As akh points out, this would remove any option that the parents could claim an accident had occurred. I also agree with akh on the ransom note -- I think both parents thought JBR's body would be found much sooner by the police. I think PR peering through her fingers at officer French is indicative of that as well -- I think she was just waiting for him to "hurry up and go to the basement and find her already!!" in her mind. I also think BR is the one who caused the vaginal injury to JBR that night. We know that injury caused some bleeding, so this would have taken place prior to the strangulation (when her heart stopped beating).
So I think the chain of events was:
1. During an argument/squabble, BR grabs JBR's shirt collar, twists it in an attempt to gain control of her as she is running away (which caused some of the neck injuries), and then grabs the flashlight and bashes her in the head.
2. The head blow caused JBR to fall unconscious to the floor immediately.
3. BR is now in "oh *****" mode -- realizing that he has seriously injured his sister. He wants to hide what he did -- but he's also a kid, so he's not going to be terribly sophisticated in this effort. It probably never occurred to him to just tell parents that JBR slipped and fell or some other lie. So he drags her downstairs (pulling by her arms over her head) and into the basement. This is how JBR gets the shoulder bruising and leg injuries.
4. We know that between 45 minutes to 2 hours passes between the head blow and the strangulation. Dragging JBR's body downstairs and into the basement would take some time and some effort for nearly 10-year old BR. Now that he's got her in the basement, he wants to see if he can revive her somehow. So he pokes her hard with the train tracks several times to try to wake her up. This is the cause of those injuries to the body.
5. When poking her doesnt work, he becomes even more aggressive either digitally penetrating her or using some other object. I believe BR was a deeply, DEEPLY disturbed adolescent already (scatological behaviors, deep-seated rage/jealousy) and I also believe it likely that he had already experimented a bit with this sexually abusive behavior toward JBR in the preceding months, but not to this extent.
6. Either in a final act of rage or perhaps because he detected *some* signs of life still (death rattle breathing or something similar), he decides he must finish her off or she will tell. So he fashions the garrote and strangles her. (The deeply imbedded cord in JBRs neck suggests such rage to me I dont believe either JR or PR would have been capable of doing this to their daughter not even to save BR).
7. At this point I think BR tries to creep back upstairs and go to bed but PR hears a noise (shes still awake packing upstairs) and goes to check on the kids, only to find JBR gone. Or, maybe BR decides to tell PR a lie that he thought he heard something, hoping that his mom will believe a bad guy broke into the house and did this to JBR. But however it played out, I think *this* is when PR became frantic and was rushing about the house acting psycho saying Wheres my baby? Wheres my baby? (Fellow Websleuther JohnJay originally came up with this explanation, and I think hes right about this.)
8. So by the time PR and JR discover JBR in the basement, she has been strangled, obviously murdered, is already dead, and theres *no way* to pass this off as an accident. And they know who did it. And they have to cover it up. So now the staging begins. (Cleaning the body, wiping off fingerprints, writing the ransom note, turning JBR over on her back to place the tape and the too-loose wrist ties, etc.)
9. I dont think removing the body was ever even considered by either JR or PR. I think they wanted the cops to find the body early in the morning, conclude it was kidnapping gone wrong, and then the family could get on with their grief and dealing privately with BR. But when the cops DIDNT find her right away, and the hours ticked away, that gave JR more and more time to think about all the things they might have missed. All the ways that the staging might have left clues behind. So when he has the chance to search the house from top to bottom, he jumps at it making sure Fleet is with him when the body is discovererd, but also making sure to contaminate evidence by removing the tape, removing the wrist tie, touching/moving the body, and laying the body on the floor.