Not sure if anyone has floated this version of the “motive” but I started thinking maybe the immediate Murdaugh family of 4 was starting to fracture into 2 camps - AM&BM versus MM&PM. AM feeling his authority is being encroached on by MM and PM snooping into his pill stash and calling him out. MM is really upset and increasingly worried about the boat case, the community shunning, the possibility of her youngest (always the baby even as an adult) going to prison for a significant portion of his life, and the looming financial exposure of the wrongful death civil cases. The “what’s for dinner” emails between MM and PM really struck and saddened me because it shows at the end of the day Paul just wants to see his mom and have a home cooked meal. Now this is totally speculation, but MM has 2 problems to solve - 1) husband on drugs, more awareness on her part about finances, concern she isn’t in the loop about the real state of affairs financially and 2) AM’s financial and drug distractions are impairing his ability, in her mind, to solve the “what to do about Paul’s” legal situation. Normally she would stay in her lane when it came to legal matters, but she starts to stray into AM’s territory. MM is taking Blanca and her sister into confidence. Maybe MM was on the verge of trying to take over control of the finances and Paul’s legal situation in a very non-Murdaugh fashion - with honesty and possible admissions of guilt, contrition or responsibility. As a mom, you would do anything to protect your child, but AM was acting recklessly. Again speculation- but if MM in the role of more responsible parent is making noise about trying to settle the civil case, liquidating property assets, and maybe thinking about a plea in the criminal case, this threatens the Murdaugh dynasty which is on the brink of being under AM’s “watch” with his dad dying. AM cannot risk MM inserting herself into matters that should be left the men in the succession of the legacy. The pill research and texts show PM and MM were outing him which with AM’s personality type starts to feel very, very threatening; so much so AM is going into self-preservation mode; is there an “intervention” in the works. This is an existential threat that unfortunately calls for drastic measures. His wife is becoming “the enemy” with her prying and the youngest, detective, is enabling her; so those 2 are acting in concert in a very non-Murdaugh manner. MM is acting normal so as not to tip off a confrontation with AM that may be coming. Weighing his options, AM rationalizes that the oldest son has to be the one to survive, so he has to protect Buster at the expense of Paul. And sadly MM is way out of her lane, how dare she, and well, he doesn’t have a choice. The Murdaugh’s are a southern variation of the mob, and killing within one’s family, in the name of loyalty to the dynasty family, is one’s duty in that twisted paradigm.
All speculation - but looking at it as AM & Buster versus MM & Paul kind of struck me today.