I was trying to make the point that "knowing" someone does not necessarily mean one has access to very private/personal things. Even a hired-hand wouldn't know. A LIVE-IN housekeeper or LIVE-IN nanny MIGHT know some of these things. Not as well, though, as the murderer knows or knew.
I think you made your point quite well, and it's a vitally important point. Everything we in the general public have been led to believe about this case suggests that the killer was someone either in the family or close to the family.