In Agatha Christie's murder mystery And Then There Were None, the identity of the murderer is revealed in the novel's final chapter. Common to Christie's mysteries, as well as to those of other mystery writers of her era, especially the writing team of Ellery Queen, the final chapter of her novels tended to provide a neatly-packaged denouement in which the story's main protagonist, usually one of her regular "detectives," Miss Marple or Hercule Poirot, would methodically present the case pointing to the guilt of the actual murderer. In And Then There Were None, however, no such denouement is possible. Instead, Christie employed a different method, one in which the guilty party's identity is revealed through a note deliberately left for others to discover. The author of that note is Justice Lawrence John Wargrave, who had invited the others to his island estate where he had arranged for the murder of each guest, including Dr. Armstrong, who had accidentally killed a patient while operating under the influence of alcohol. At the end of Wargrave's lengthy note, he writes:
"During recent bouts of pain, I had been ordered a sleeping draught -Chloral Hydrate. It had been easy for me to suppress this until I had a lethal amount in my possession. When Rogers brought up some brandy for his wife, he set it down on a table and in passing that table I put the stuff into the brandy. It was easy, for at that time suspicion had not begun to set in."
Wargrave manipulated the feeble-minded physician into helping him carry out this series of murders. Armstrong did not murder Mrs. Rogers; Wargrave carried out that evil deed.