NP Who really did kill Roger Ackroyd?

[jbor]

http://www.smh.com.au/news/0102/24/books/A22734-2001Feb16.html    

    "Tellingly, Bayard's new solution addresses what is generally regarded
    today as the major weakness of the Golden Age crime novel, its
    inadequate characterisation - for it is the psychological implausibility
    of Poirot's solution which most worries him and his answer convincingly
    satisfies his reading of the psychic forces hidden beneath the surface
    of Christie's text."

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