While it makes little sense narratively, I’ve noticed that you never used the red to state that Kanon went directly to the guest house after leaving the dining room, which is also supported by the text, given that he glanced into the parlor even though the parlor is in the opposite direction.
I repeat my blue truth that in this timeframe after Kanon left the Dining Room and before he left the mansion, he killed Rudolf. He then hid the corpse somewhere and constructed the closed room the next morning.