The books grandma gave (ie Teaching children right from wrong) is also a clue. (source... bonita papers) Something was up and not quite right and grandma knew it. All parents will be in denial. Mine were. I suffered severe physical abuse from a sibling at an early age until my teenage years and each time it was excused as an accident or the sibling "just being a kid". (I was stabbed with a stick in my crib by this sibling when the sibling was just 4 yrs old and I was of course an infant) My sibling wanted me dead.(still does. but after adulthood it becomes character assassination in the extreme form... even going to my neighbors and bosses) Every broken bone and stitch was excused away. I learned quickly never to be alone with this person. Unless you have been raised in a dysfunctional family made that way by a child born with a mental disorder (which I believe B as well as my sibling was), you won't see what I do. If you haven't experienced it, I'm glad you did not live what I have. My theories may seem absurd by many, but I have them. It has been suggested that she was abused in the past, be it "playing doctor" or whatever. B, in my mind (my opinion only), experimented on her and she irritated him at every turn. Be it touching pineapple with poopy fingers or else. In my mind, she screamed (was it touching pineapple or the forceful vaginal jabbing with a paint brush?). A bash on the head with the flashlight to shut her up? Who knows. (doubtful any of us will ever really know) Was he experimenting with or curious about strangulation? (my sibling was obsessed with mummification at that age... you know, all the organs being removed and all). They were boaters and surely he had learned knots by that age. this is just my two cents. My sibling at that age had incredibly strength to do similar if in a "rage".
I would love to find out that it was indeed an intruder. Would love it, but so far, nothing is convincing me. So fire away. Thanks in advance.
All the above is just my opinion and theory.