It's hard to know what these proofs imply: other than that there is a lot of odd history with the Riccis, which hardly changes the water on the beans.
As for the Smarts - that's the sort of thing where you do really need to have a bit of backup, and shouldn't be too dificult to find if there were anything in it. You'd expect National Enquirer or one of the ranker publications would have something on this, since the family has been in the spot light for so long.
There's been a lot of talk about various theories here, and some of them are quite wild. People say "theory" when they apparently mean "hypothesis". To qualify as a theory, the explanation of a set of your observations has to be based on principles which are independent of your observations. What you've done is offer some more observations (of uncertain veracity), which seem almost intended to spawn more fanciful hypotheses. I don't say you meant to do only that, though.
About Mary Katherine's story: In general you can doubt a story, but you can't discard it unless you have some better alternative. In this case there isn't one.
About lies by the police, the family or whomever: At the very least, it's not much use to assume someone could be lying: that's actually the wrong way to find out if they're lying. If you want to find out whether someone is lying, it's better to take their story as if it were true, rather than infer otherwise, and then take each piece at its face value and see where it goes. If it is untrue, things will stop adding up pretty soon. If someone says "I was at the movies last night!" you don't say "I don't believe you", you say, "Yeah?What did you see?"
As for people here who doubt the wilder hypotheses, it doesn't strengthen the case to accuse the doubters of conscious or unconscious complicity in a coverup. The wilder (and less well-founded) a hypothesis is, the less convincing it is. Without indications of the contrary, you must assume good faith in someone's doubt.
Lastly, I was reading a book about serial murders the other day. Dreary stuff. No complex, mysterious plots. Simple, barbarous crimes, and most went unsolved for years. And how did the half-sentient animals remain at large for so long? Not because they were really clever, or their crimes incredibly devious, or the police stupid or obstructive, but just pure bad luck for the rest of us, and this won't change unless we will have 24/7 video surveillance at every street corner and every exit ramp in America.