History

• iirc she doesn't have an alibi for the umbrella thing. she kinda gave a non-answer to that?
• as a servant, she has master keys.
• she was assigned to the guest house but, for very dubious reasons (being embarrassed, I guess) chose to go to the mansion, the place where the first twilight victims were staying.
• she was wandering the halls when the Beatoflies first popped up, and seemingly was the first to encounter them. This could, instead, be reinterpreted as her taking on the butterflies, 'becoming' Beatrice (a bit of a stretch)
• she died in the first twilight, meaning that if she pulled a fast one then, she has free reign and is without alibi for the rest of the spree.
• her corpse had a half-smashed face. to borrow battler's insistence on chessboard thinking, this is suspicious to me, as assuming a layered motive on the presentation of the first twilight, the smashed-faced victims are going to be immediately thought as suspects due to the ease to pull a dummy body trick. The half-smashed faces, on the other hand, are immediate signals that these are, in fact, the bodies of these people. HOWEVER. these cadavers could be disguised as well, with makeup used to shape the face differently to the eye— especially in their grisly state, which people don't really want to look closely at. furthermore, due to the extreme nature of the scene, no one wanted to get close to the bodies or touch them, lest they fuck up the police investigation. George, the person who was the closest to Shannon, did not look at her face. Rather, Hideyoshi was the primary examiner, and from a distance. I also find it suspicious that Shannon's body was off in a corner whereas everyone else was in the center. Maybe her face was not in the light?
• I do not believe that Hideyoshi and Eva's room is a true closed room, despite the dogged insistence on it. There's a very large floating assumption that the chain has to have been latched from the inside, but if Kanon has enough room to stick wire cutters into the door to cut the chain, Beatrice/Shannon has enough room to snake a hook in to latch onto the chain, then latch the chain to the anchor on the wall by angling the hook from outside the door. Honestly, this is a stupid assumption for the characters to make, but I'll permit it because it's intriguing and a realistic assumption at that level of stress
• Kanon was the first person to see the sigil and pointed people to the Rose Garden storehouse. This can be reinterpreted as either Shannon or Kanon drawing the sigil and then dispatching Kanon to get everyone else.
• this covers Kanon's really fucking weird death, because we could then assume Kanon's perspective is unreliable narration. Kanon, technically, could also be a disguised cadaver, but I think it's a bit more dubious given Nanjo operating on him and them being kind of alive.
• Kanon had direct access to Kinzo in a scene prior. While Genji is seemingly the only one with a key, the servants are given freer access to Kinzo generally, and due to Kinzo's mental state, if Shannon is disguising as Beatrice, he'd probably fold immediately.
• at that point, there are eight people left, and they all have heightened emotions. They enter the study. If she isn't there, due to Maria's easily impressionable mind, 'Beatrice' could have extracted a promise from Maria to place down the letters when no one was looking and pretend she wasn't behind it, lest she not go to the Golden Land. If she is, then it's a bit contrived sleight-of-hand and stealth.
• Then, 'fulfilling her promise' to Maria or choosing to spare her for other reasons, she kills the other three servants. Or maybe she convinced Maria to do so, if we assume Maria's narration is unreliable due to her being 9 and a little obsessive with extreme fantastical thinking. Maria is essentially entirely compromised, whether she's in on the ruse or (likely) not so, but wanting to believe in witches. She then calls Natsuhi, luring her out of the study she cannot yet access due to the key being in Natsuhi's hand
• Finally, as Maria's creepiness distracts everyone, let's say she pickpockets Natsuhi and drops a letter by her, dashing to the study.
• Do we even know if there aren't, like, two guns? We know there's one gun, but the assumption that Natsuhi either got perfect-parried or shot herself doesn't hold up when we cut to Battler immediately as a gunshot was fired. just the sound echoing. plus, the language in the characters page implies a duel, which leads me to believe equal starting conditions.
• Finally, everything is left up in the air when 0:00 strikes. For the concrete things, Battler could have very easily missed his shot, it's nighttime and emotions are heightened, and he's also eighteen and probably doesn't know how to handle a gun. Furthermore, we never actually see who Beatrice is, she's only implied by the narration and the painting

This doesn't mean I fully say Shannon committed all or even any of the murders. Honestly, in some cases, she may have even just convinced others to commit murders and then set it up posthumously to look magical. To be honest, the situation is ripe for a lot of stochastic revenge kills under the guise of Beatrice doing so.