About the Ramseys being at a Christmas party and where was the babysitter...
The Christmas party they had been at WAS A PARTY THEY HOSTED IN THEIR OWN HOUSE.
That was one of the problems in investigating who had access to possibly doing the crime, because this was a huge affair with many people coming and going that evening.
Besides that problem, the Boulder police clearly believed the parents were the culpable ones, and that (focus on the Ramseys) did simplify what would otherwise have been a very complicated investigation, to say the least.
That would give him access to the layout of the house....and no one would notice.
So there's the possibility that Jon Benet KNEW the perp but he was obscure to almost everyone else at the party.
No it wasn't. The party that night was at Fleet and Priscilla White's house, several miles away.