Here's the problem though:
We know the study is off limits. This may or may not be tied to Kinzo's body, but generally speaking nobody should have any interest in going in there nor should they be permitted unless they are Natsuhi, Genji, or Nanjo. If the letter was pre-placed, any of those three could have done it (assuming that Nanjo was hanging out in the study at the times he claimed to be, anyway). Shannon/Kanon may or may not also be possible.
Why place the discord letter in the study if you aren't anticipating anyone will go in there? And if you
are anticipating it,
how do you know when, why, and who will be going in there and find it? The letter seems primarily useful in driving suspicion (Maria's explanation of the magic circle in particular). Suspicion seems only valuable if you already know ahead of time people would go to the study to hide, and that the group would be large enough to separate.
I see the following scenarios as possible:
- The letter was always there, people just didn't find it. Kinzo intended it be used for something and never got around to it.
- The letter was pre-placed earlier in the day, perhaps to be part of an "epitaph game." Maybe Kinzo was supposed to "vanish" and his study entered.
- The letter was pre-placed earlier in the day, and Natsuhi was rehearsed to move people to the study at some point during the game. Natsuhi did so without realizing what was going on. Because the group was always intended to travel to the study, the letter placer knew ahead of time who would be reading it and under what circumstances.
- The letter was placed on the spot in accordance with the script, perhaps by someone like Maria who would not realize it was inappropriate at the time.
- The letter was placed on the spot in accordance with the script, by a person who knew full well that the murders were real but who wanted an excuse to either flush suspects out of the study or who wanted an excuse to leave the study themselves.
- The letter was placed on the spot by a collaborator with the killer, who had the letter in case people would try to hide in the one place the killer does not have the freedom to enter (the study). This necessitates the collaborator remain with the group and always maintain an airtight alibi, which basically limits it to Jessica or George.
- The letter was placed by the killer. Genji, Kumasawa, and Nanjo were faking it in the parlor in accordance with the script (and possibly trying to lure out the real killer when he/she arrived to "re-kill" them).