>I don't think we will ever know much more for sure but I am reasonably certain there are (or were) people in the Kennedy family who knew much more than they shared and people in the intelligence community who had some very well founded suspicions which they occasionally shared with interested young hangers-on.

I really love the haunting possibilities, but for me the killing of Bobby tends to act as Occam's razor:
if that much sinister play behind the scenes was going on in Dallas,
I'd never expect someone like Shirhan to succeed - I would expect a dead Shirhan,
as Bobby then would not believe even perhaps honestly meant "JFK was enough for us"
sentiments if such were uttered, but would have keept his guard better up,
pairing people from different sources to check on his safety and each other.