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In Agatha Christie's book The ABC Murders, what is Cust's possible motive for each murder? Why would Cust write letters to Poirot before each murder? How might Cust profit from each of the murders?

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In Agatha Christie's The ABC Murders, Alexander Bonaparte Cust appears to be the serial killer, a man with a motive that might be no more than going through an alphabetical set of murders designed to puzzle one of the world's greatest detectives, Hercule Poirot. However, Cust's involvement turns out to be a red herring. Let's explore what happens.

Cust actually seems to have no motive at all for killing anyone, other than the possibility mentioned above. He is a veteran of the World War I who suffers from blackouts due to a wartime injury, and he has been hired as a stocking salesman who happens to be in the towns in which the murders occur. Cust has no memory of writing letters to Poirot or of committing any of the murders, but he thinks he might have done so because of his blackouts.

Actually, though, Cust is innocent. He is being used, set up as a cover for the real murderer, who is the brother of the third victim. Franklin Clarke has set up the whole scheme, including hiring Cust to be a salesman and the fall guy, in order to kill his brother so as to not be disinherited. The motive is, as it is so often, money.

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