Sure, it's not proof, but who else in the house had the smarts to compose drafts of the ransom note, all nicely structured, incorporating unusual keywords and phrases, e.g. "Don't grow a brain", etc.
No intruder is going to sit down to author a ransom note in the middle of an abduction, he/she would come prepared with a note in their pocket?
It's all staged, wine-cellar, ransom-note, the 911 call, one big hoax to deflect attention away from the Ramsey's.
The minimal conclusion is that all three Ramsey's were involved in postmortem staging?
John gives the game away by phoning for his pilot so he can flee interstate using his private plane.
Would an innocent man do this, including leaving his daughter's body behind?
.