"Do you know why a triangular relationship is the most stable?"
"Because it has two points of support? Whenever one side tilts, there's another point to help support it, or shall we say, to keep it in balance?"
"No, because a triangular relationship is the most ambiguous, you'll never know if your 'he' is his 'her,' or her 'him'? Cough, in short, when there are too many possibilities, when everything is based on guesses, you naturally hesitate to make a move."
"Guess?"
"Yes, guess. When coming out, guess whether it was A who did it, or was it B pretending to be A, or A pretending to be B pretending to be A, or B pretending to be A......"
In a case, the murderer could be the beneficiary, or the one harmed pretending to be the beneficiary to secure a more long-term benefit, it could be.... the nesting dolls are limitless.