Well that is also part of my theory. I think JBR's body was initially concealed in the trunk of one of the R's cars, or possibly in the crawl space in the train room - which could be why JR put a chair in front of door, hoping to prevent anyone entering.
At that time it was a 'simple' kidnapping - their daughter had been taken so the couple would not have expected anyone to search the house. They had already told the police they had looked everywhere - why wasn't that enough?
The plan was that when the phone call did not materialize then naturally the police would leave the Ramseys home. The couple could then bring the body out, leave her in the cellar and then make another call to the police saying they had discovered their daughter's body - dead. The kidnapper had killed her and returned her body to them because they went against instructions and had called the police.
Unfortunately the plan went wrong. The police showed no signs of going. John knew that if a thorough search was undertaken then his daughter's body may be discovered in his car. He HAD to bring her back inside, which he did. He put her in the wine cellar - this accounts for his 'missing' time.
He went back upstairs and as soon as Arndt suggested another search John was up out of his seat and straight down to the cellar room where he 'discovered' JBR.
You know the rest.
Miz Adventure.
Sure it was likely something along these lines. My BDI is similar but BR, unlike in Kolar's theory, does not do it all. JR and PR help him out by smoothing away a lot of forensic evidence.
I reckon the R's game plan was simple, i.e. hide JonBenet, fake an abduction to explain this, hope she is not found, then escape interstate as soon as possible?
.