Very likely what Krauss went to the storage room to retrieve is what cut George’s hand - i.e. the knife that killed Kinzo, stashed away in the vent. This means that Kinzo was still alive when the knife was in the vent, at ~9:31. So, let’s begin:
[color=blue] The culprit is Krauss. The only window he’d have to kill Nanjo is before the discovery of either Rudolf or Nanjo’s bodies. He has no alibi (in purple) for his time in the parlor, so lets go with the easy solution and say he snuck into Nanjo’s room shortly after Rudolf is locked up, suffocates him, takes the key, and leaves. He drops it back into the room via the vent in the medical office. This could all be accomplished under the guise of a bathroom break or the like during his time in the parlor with the other siblings. [/color]
[color=blue] Next, Rudolf sneaks out of the tower with the intent to find the will, now that Kinzo is out of the study. He accomplishes this using some sort of climbing equipment he had hidden in the fake ceiling of the tower, which would drop down when he removes the stone noted in O’s note. He also prepared the trenchcoat and hat to shield himself from the rain. Rudolf falls from the window, sustaining minor injuries. He sneaks into the mansion, enters Kinzo’s study and ransacks it, finding the will. He then evades Kanon and jumps out of the hallway window down into the dining room window. He is knocked out by Krauss, who spots him on his way to the storage room. Krauss carries him back to the study, and kills him there. This route evades Natsuhi’s vision. [/color]
[color=blue]Krauss retrieves the knife from the storage room and hides it on his person. He also hides the trenchcoat and hat he took from Rudolf’s corpse. In between the time when Jessica screams and when the entire group gathers at the study, Krauss slips away and kills Kinzo, entering the passage via the servant’s room (after Gohda is lured away by Jessica’s scream). This is before his alibi in purple is valid. [/color]