With Season 2 of Big Little Lies coming to an end, I'm afraid the show won't answer all the questions I have about Perry and Mary Louise. His deceased twin brother, Raymond, has been referenced a few times, but the circumstances surrounding his death are still unclear. These details are important because they paint a clearer picture of how Perry became the abusive husband he was to Celeste. That said, it's not a stretch to wonder, if Perry killed his brother. Big Little Lies has some explaining to do.
A Season 2 flashback of Perry and Celeste maybe offered up a clue as to what was going on in Perry's (obviously troubled) psyche. Celeste admitted she's an only child to a deceased mother and father she has no relationship with. Perry pounced, saying, "I don't mean to be presumptuous, but if this works out, I would have you all to myself." If you add this to Perry's violent and aggressive behaviors, it's easy to assume he could have become obsessive and violent with others, too. Perhaps even his own mother, and therefore had to rid himself of his twin brother to have her all to himself. It might be a stretch, but who really knows. One thing fans know for sure is that Perry was dangerously violent.
Now that Mary Louise is poking her nose in everyone's business, the Monterey Five aren't the only ones with secrets. I don't buy that she's at all innocent. She's either in denial about who her son was, or she contributed. She's clearly unwell in multiple ways (grieving aside), but this theory suggesting Perry killed his brother only works if Mary Louise was willing to look the other way or make excuses for him — just as she's done when Celeste admitted Perry "beat" her. Mary Louise is quick to deny any wrongdoing on Perry's part, making everyone else the problem. She did as much with Jane, saying the assault had to be Jane's fault. Perry could get away with an "accident" involving Raymond if Mary Louise refused to see then what she refuses to see now: that he's the problem she may have created.
If Perry isn't responsible, I think Mary Louise is. She has serious serial killer vibes happening and the mention of "an accident" is a little too vague when referring to the twin brother of a violent man and his unwell mother — a mother trying to get custody of Celeste's twin boys.
I'm not saying Perry definitely killed his 5-year-old brother, but I'm not not saying it, either. After seeing the way Mary Louise curiously (and rudely) interacts in the world, as well as her odd and obsessive nature, there's no way BLL writers should expect fans to believe the boy died in an accidental way. Perry did it, deliberately, and Mary Louise covered it up, or Mary Louise did and created the monster in Perry.