Lots of credible comments in the last few posts. Money, time, reputations, questions, questions and more questions have all contributed to this crime being left an open cold case.
Bottom line, for me, is charge JR with Felony Murder. It doesn't matter then who did what - just that he was there, aware, and did nothing to seek an interruption in her death makes him a party of Felony Murder. IMHO, circumstantial evidence, combined with forensic evidence, is strong enough to convince a group of 12 jury members with half a brain and a complete soul that JR bears responsibility in JB's death.
He can't prove he WASN'T the one who killed her, can he? Those shirt fibers in her underwear are more than very incriminating, IMO. Absence of any other fingerprints on suspected weapons makes him just as likely to have used them as anyone else. And, before police told them they would have to leave the house, he called to arrange for a flight out of state.
Good thing I wouldn't have to be on that jury.