Since this has been bumped, and people are considering JARDI theories, may I point out Cynic's post #11, and Agatha_C's post #56.
I would also point out that if JARDI, no fewer than 7 people are involved in providing a false alibi for JAR. While it's believable that LR and MR might lie to protect JAR, and maybe SL is sucked into doing the same, it's much harder to believe the other four were close enough to be willing to make false statements to police to help JAR get away with murder.
Brad Millard was a friend. Good enough friend to lie to the police? Good enough to fly JAR to GA in the wee hours of the 26th thus making him an accessory after the fact ? IMO not likely.
Chris Stanley. Same as above.
Harry Smiles. He was a friend of Lucinda's. Why would he feel a need to lie about JAR's presence in GA the evening of the 25th?
Judy Crowder. Neighbor who hosted Christmas dinner attended by Lucinda, MR, SL, and JAR. I'd think it's very unlikely she was willing to give JAR a false alibi.
A rational person would have to conclude that it's unlikely 7 people agreed to provide JAR with a false alibi.
JARDI doesn't fly, it just doesn't have wings