I doubt they recovered Maria’s diary from the island, as well… if they could only recover maybe pieces of people, it’s doubtful they would have recovered a fully intact diary. Perhaps the diary was found at Rosa and Maria’s home? And I think it’s stated in the manga of EP8 that Bern’s “Ange does not live past 1998” in Red was a playing with words, since in the Magic End, Ange essentially kills that part of herself to live as Yukari Kotobuki. I imagine people must have been surprised that Rokkenjima was covered in landslides due to the explosions, and as for why the police being unable to find the details of the murders and why they only found Maria’s jaw… I’m not entirely sure?
Also, in hindsight, it’s hilarious that the biggest theme of Umineko is dropped by a character who isn’t even a main character.
But EP4 really seems to be where Tohya tried to humanize Beatrice the most with her relationship with Maria. You can see her fondness for Maria and how it upsets her with Ange denying Maria’s magic, as well as how it breaks her heart to see how Maria’s heart was torn to shreds with Rosa destroying Sakutaro. Their relationship is adorable and symbiotic, which makes it all the more heart-wrenching when Beatrice can let Ange fool Maria in the end or be selfish and tell Maria the truth to keep Maria by her side, and she chooses Maria’s happiness (and on the actual gameboard side, Maria’s corpse is displayed in a manner that Battler can tell that her killer cared for her). You can tell that the writer from EP3 onwards very much tries to humanize the person behind the mysterious murders, and while EP3 was about her relationship with Battler, this one opened up on her relations with others.
And this EP put a lot of new revelations on when it came to Maria. How her kihihihi is actually a coping method where she murders the person who offends her in her mind, repeatedly, as a dark contrast to her previous coping method of having imaginary friends to create a perfect illusion to not feel alone. How Maria is so broken by her life with her mother that she prefers a world that she can only reach by dying, where she can finally have that dream of a mother who only dotes on her and has all the time in the world for her. And what the real icing on the cake for what makes Maria so tragic is the circumstances of Sakutaro and why Ange was able to “resurrect” him. And the whole fact that Maria had broken the chain of abuse, even if just for a bit, by pretending, I can’t help but cry over a nine year old’s strength.