Out of all the ideas that have been tossed out about the perp(s) and motives, this one makes the most sense. Some one had mentioned two males who are unrelated to the Murdaugh family, that were alleged to have been at/participated in the SS tragedy. That would explain two different guns used during the murders. And tie up the on line threats to Paul. Murdaughs never pursued the threats bc that meant Paul and Buster would be implicated in SS death. But if it came down to Paul being guilty in Mallory’s death, and going to jail, Maggie and Paul would throw the other two males under the bus. The deal would cover Buster and Paul, and hang the other two males. It was getting a little too close for comfort, so the two males took it upon themselves the get rid of the problem: Paul and Maggie, both. And that, my friends, is what I have deduced.
ETA: grammar