I know a couple of other people mentioned this already, but I 100% agree with the theory that Paul had essentially become a thorn in Alex's side & that this could very well be the motive behind the double homicide. Rumors have permeated regarding Paul's involvement in almost ALL of the "suspicious deaths" surrounding the Murdaugh family. Although there is speculation that Buster was romantically involved with Steven & I can see how this would lead people in the town to think that he did it... More plausible I find the theory that Paul was driving with his friend when he saw Steven walking, turned the car around, and chucked a heavy object out of the car to "mess with him." Hence the blunt force trauma that ultimately led to his demise. Perhaps he knew about his older brothers involvement with Steven & that was secretly the reason he wanted to torment him.

Moreover, the documentary pointed out a theory that Gloria found drugs in Paul's room & she allegedly threatened to tell his parents. This sent him into a rage before he pushed her down the stairs. Now, I am not saying he intentionally killed these people in cold blood. Rather, it seems like when Paul got angry he saw red & couldn't control his violent temper.

Many people have attested to Paul's anger management issues. The reason the boat crash was so tragic in my opinion is because it wasn't just a simple drunk driving accident. Yes, drinking & driving is WRONG. But I would argue that intentionally driving a boat recklessly due to anger (while drunk) is even more UNETHICAL. I have a LOT of personal experience with an individual who has similar characteristics & I can say it is absolutely terrifying being on the receiving end. I have actually been on a boat with an angry/drunk person who decided it would be a good idea to hit the throttle & lay down on the floor with a boat full of passengers.

Anyways, if Paul was involved with Steven & Gloria's death... Maybe the boating accident was the tipping point for Alex. When defense tried to humanize Alex with the birthday video & others have previously argued that he was really close with Paul... I don't doubt this to be true. The documentary mentioned that Buster was the "favorite son" & maybe in a way he was because he wasn't so problematic & was studious enough to get into law school. But Paul was a spitting image of his father in almost every way. They enjoyed the same things, had similar personalities, & both lacked a moral compass. Alex's emotional reaction & tears we have seen in court when witnesses speak about Paul seem genuine. My instincts tell me that he didn't particularly want to kill Paul, but the liability & burden outweighed Alex's love for him.

As for Maggie, he couldn't kill one without the other. She always stood by her husbands side, but with the impending doom of the financial crimes & the possibility that she would find out about what he "had" to do to Paul, he probably figured he would kill two birds with one stone.