Chrishope,
JR himself rejects the via the basement window option, so if its an inside job why did the insider not leave via the front door, and how did they know about the wine-cellar, and where the size-12's were located?
It sounds like JR is blaming JAR, or a past babysitter to JonBenet?
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JR rejects intruder through the window initially, but after LS effectively starts playing for Team Ramsey, he goes along with the intruder through the window nonsense.
On the 26th he is at pains to make sure everyone knows he himself broke the glass in the window, supposedly when he forgot his key and had to break in through that window. He isn't fingering anyone at this point, he's just explaining the break, because if he doesn't explain it, even BPD will start to figure out it looks like a half completed staging job. He knows at that point that the body will be found (he probably doesn't think it will take 7 hours, but he knows the body is going to be found) So he'd have a dead girl, a broken window, a RN, and it would look for all the world like he (they) were staging a break in/kidnapping to explain JB's disappearance.
Months later, when he finally decides it's time to help police find the killer, he suddenly "remembers" that the window's frame was ajar, and that he closed it. He doesn't know why he closed it, and he doesn't know why he didn't mention this to the police on the 26th -given he and the cops were discussing the security of doors and windows one wonders why he didn't mention it while it was fresh in his mind. At the interviews he also now can "remember" that the suitcase is out of place. Again something he "forgot" to tell the police the morning his wife called 911.
So it's pretty obvious that on the 26th he's saying "No, no way did anyone break in. All the doors and windows were locked, and the broken window in the basement, well I broke that myself, so it had to be an 'inside' job." That's not a quote of course, that's the essence of how JR is trying to shape the story. Months later the story has changed to "Yes, I broke the window, but now that I think of it the frame was ajar, and the suitcase was under the window, and an intruder could have come in that way, yah, that's the ticket, and intruder came in that way." Again not a quote, just showing how the story has changed. He's trying now to give some plausibility to the intruder through the window theory.
It doesn't sound to me as if he's blaming JAR or a babysitter. On the morning of the 26th he's just making sure no one is thinking he staged an intruder through the window because it's obvious no one came through the window. He'd be arrested if the cops could put it together on the spot.
A babysitter wouldn't likely have a key, but if she did would she also know where the WC is, and where the 12s are? No reason to blame the murder on such an improbable perp.
As for JAR, JR knows he's in Atalanta or winging his way north for the meet up in Mich, so it makes no sense for him to try to point a finger at JAR. JAR has a pretty good alibi.
As your questions make clear, an "insider" seems unlikely as that person would have to have locked the door behind him (why bother) would have to know where the WC is, and would have to know the 12s were in a package in the basement -if in fact that's where they were. As implausible as an insider is, he switches to the even less plausible intruder through the window theory with LS's assistance. If he's got LS in his corner, pushing the window break in theory he can't very well disagree.