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Grammar as a clue in an Agatha Christie mystery
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Was there ever a case where it was solved by analyzing the criminal's note and realizing that the grammar usage meant that the individual was of a certain background or education?
edited December 2018
I wondered if this picture might interest you. Agatha Christie was all about Poisons as a murder weapon, based on her background, however, her murderers did not always comply with her wishes. This year the BBC have a Christmas Christie drama, The ABC Murders, you will see that the written word does play a part in solving the crime, but in most cases, it was the murder weapon that took the front seat. (Sorry if the picture is not very clear, I'll try and find where I got the original.)
Not the criminal's background exactly, but in "The secret Adversary", Tommy realises that a note he received, that was supposed to come from Tuppence, is not from her because her name is spelled "Twopence" on the note, while Tuppence - and probably most britishers - would spell it Tuppence (It actually means two pennies).
In another author's book from the same period, "Final Curtain" by Ngaio Marsh, Troy realizes that Panty, the troubled little girl, did not write the message mocking her grandfather, because it includes the word "Grandfather", and she has seen Panty's writing, where she spelled it "Grandfarther".
Gloucestershire, United Kingdom
There was an incident in a Morse story (I assume it is the same in the book as well as the Adaptation but when Lewis says something to Morse realises that someone wouldn't have said what she is supposed to have said and so she isn't guilty of a Murder lthough she is Guilty of a Lesser Crime, this is in the Murder set in a Brewery.