Not an answer to your question but I watched the HBO documentary recently, too, with my wife who is an investigator/attorney. She hasn’t really been following the case so this was her first real introduction to it.

She was struck by the jailhouse call between Alex and Buster where Alex keeps suggesting Buster go hunt doves at Moselle, to hunt them at a specific place at Moselle, and if he wouldn’t, he’d send someone else there to hunt. She found Alex’s words, and Buster’s reaction to them, really strange, and wondered if they were speaking in some sort of code. She thought he was really telling Buster to go to Moselle to get something, maybe something he’d hidden there.