In 'The Catbird Seat' by James Thurber are the cigarettes a plot device?

The cigarettes are a plot device because they are necessary for the successful completion of Mr. Martin's plan to get away with murder. The cigarettes would create a smokescreen to cover his involvement in snuffing out Mrs. Barrows. The police would suspect a smoker as the one who lined her up for 20 coffin nails. His reputation as a non-smoker would ensure that the police would never consider him a suspect.