Following Louise's funeral, Amy meets with Miss Johnson on the house's roof, whereupon she claims how someone could have entered unseen but does not elaborate on this. That night, Miss Johnson unwittingly drinks a glass of hydrochloric acid that had been substituted for her usual glass of water on her nightstand. Amy comes across her, and hears her hint to the window before she dies; the nurse doesn't believe she committed suicide, and wonders if she was hinting to how the acid was switched for the water. After spending a day sending telegrams, Poirot brings everyone together and reveals that both women were murdered by Dr Leidner, who is in reality Frederick Bosner. In the aftermath of the train crash, Bosner came across the body of the real Erich Leidner, and seeing that his face had been disfigured, stole his identity in order to escape the authorities. Poirot reveals how the murder was committed from the rooftop; after attracting Louise's attention with a mask he used on previous nights, Bosner dropped a heavy stone quern from above, the moment she stuck her head out of her window, before pulling it back up with a rope he tied to it. Visiting her room on the pretense of checking his wife, he then proceeded to move her body and the rug away from the window, before closing it, using Amy as part of his alibi to divert suspicion away from him. Miss Johnson was murdered, merely because she had figured out how Louise was killed; her hint was towards Louise's window, and not her own, as Amy had mistakenly believed.