>>49615476Rosa being the culprit had heart though.
I personally believed she was in fact Kinzo's and Beatrice's daughter, and that she had accidentally killed her sister (Kuwadorian Beatrice) and later learned that she was her sister. Crushed by all this and her shit life in general she went on long 'vacations' where she was actually desperately trying to solve the Epitath, which she eventually did. But because of how distrustful she is even if she solved the Epitath she couldn't make use of the gold, so she came up with the plan to wipe out the family. Doing so for Maria's sake also.
Basically, a mix of doing it for money, vengeance, schizoism, and love. Trying to resurrect her sister metaphorically speaking, and masquerading the crime at the same time so that she and Maria could get away with it and live off happily from the gold.