Your assumption that a mastermind is required may not be valid. Ricci knew the victim, possibly had a key to the house, knew the layout of the house, and was a cat burglar by trade. All that was missing from a plan would be where to hide the victim and establishing an alibi. We already know that his alibi is full of holes. None of that requires rocket science.
Well, you're right about one thing--I am not a rocket scientist! And my assumption may not be valid. This guy is a petty thief and may have done this on his own. My gut feeling is that he didn't. But I've been wrong before. Ricci has spent most of his adult life in jail and with his recent marriage and steady job, had a lot to live for. Had reasons to keep his nose clean. Since I'm not a criminal, I don't think like one and may have misjudged him. But I get the feeling that LE can't pin it on him either.