I don't believe anyone came in through that window. I think the killers (plural) had a key. I feel it is possible that one or more left through that window.
Be fair, BC. FW said he was down there in the basement early that morning. FW said he found the window closed and unlatched. JR said that he went down there later, he found it open only 1/8 inch, and he closed it and latched it. The stories are not inconsistent.
You are right that the window was not open when FW first observed it, but they are both in agreement that it was unlatched, but I don't see it as being unlikely that an unlatched window can open and close in a breeze, so neither of them are necessarily lying on this point, and we're only talking about 1/8 of an inch. It could have been open that far when FW observed it, and he still could have perceived it as being "closed."
If it were a part of staging on JR's part, why didn't he open the window all the way and have more broken glass around? He says himself that it was open only 1/8 of an inch.
If he was lying, what was the point of his telling this story? He would have kept it quiet to make it look as if an intruder had broken the window. This indicates to me that he is telling the truth.
As far as JR's sneaking away, it was his house, and he was free to go into any room he wanted to, just as you are now. This does not necessarily indicate guilt, and it is not the Ramseys fault that the police did not follow the correct procedure.
Someone refresh my memory here -- I wasn't able to find this in a cursory search of PMPT. Who was down in the basement with Officer French that morning? Was it JR? Someone had told him that there wasn't an exit from the wine cellar, so neither of them bothered to look. Book and page # would be helpful.
Paradox, I disagree. John didn't lie about the broken window. He told the truth. He said he broke it the previous summer. If he were lying, he wouldn't have brought that up at all, and if someone else did, he would have denied it. That would have been lying. He told the truth about the window.