Radon

ALT All of the clues led to one possible culprit for murdering Fuji: a vengeful spirit, Fen Sawa. The evidence pointed directly to Fen: she was capable of creating ectoplasm, whose color, smell, and composition matched that of the substance found in Fuji’s body. Fen’s nature as a ghost additionally meant that she could not be seen on camera, so she was free to do as she pleased with Fuji, regardless of any security cameras present. Lastly, Fen had a motive contingent on evidence that most people overlooked: the moldy apple in Fuji’s trash can. Fen was a spirit known for her intolerance for wasted food, and seeing Fuji do so was likely her last straw. Fen refused to admit anything, and fled from the detectives charged with arresting her.