In the Teeth of the Evidence by Dorothy L. Sayers Page A

I’ve got them now and here they are. You know, gentlemen, it stands to reason, if a capsule was taken off a bottle that day in the study, there must have been a bottle belonging to it. And where is it? It’s got to be somewhere. A bottle’s a bottle, when all’s said and done.
        ‘Now, gentlemen, Mr Whipley dealt with my employers, Plummett & Rose, for over fifty years. It’s an old-established firm. And that capsule was put out by a firm of French shippers who went into liquidation in 1900; Prelatier & Cie was their name, and we were their agents in this country. Now, that capsule came off a bottle of Noyeau sent out by them – you can see the last two letters of the word on the stamp – and we delivered a bottle of Prelatier’s Noyeau to Mr Whipley, with some other samples of liqueur, on June 14, 1893.’
        ‘Noyeau?’ said the coroner, with interest.
        ‘I see that means something to you, doctor,’ said Mr Egg.
        ‘It does, indeed,’ said the coroner. ‘Noyeau is a liqueur flavoured with oil of bitter almonds, or peach-stones – correct me if I’m wrong, Mr Egg – and contains, therefore, a small proportion of hydrocyanic acid.’
        ‘That’s it,’ said Monty. ‘Of course, in the ordinary way, there isn’t enough of it to hurt anybody in a single glassful, or even two. But if you let a bottle stand long enough, the oil will rise to the top, and the first glass out of an old bottle of Noyeau has been known to cause death. I know that, because I read it in a book called Foods and Poisons , published a few years ago by Freeman & Toplady.’
        ‘Cedric Whipley’s firm,’ said the inspector.
        ‘Exactly so,’ said Monty.
        ‘What, precisely, are you suggesting, Mr Egg?’ inquired the chief constable.
        ‘Not murder, sir,’ said Monty. ‘No, not that – though I suppose it might have come to that, in a way. I’m suggesting that after Mr Raymond had left the study, the old gentleman got fidgety and restless, the way one does when one’s been through a bit of an upset. I think he started to drink up his cold coffee, and then wanted a spot of liqueur to take with it.
        ‘He goes to the cabinet – doesn’t seem to fancy anything, roots about, and comes upon this old bottle of Noyeau that’s been standing unopened for the last forty years. He takes it out, removes the capsule and throws it into the fire and draws a cork with his corkscrew, as I’ve seen him do many a time. Then he pours off the first glass, not thinking about the danger, drinks it off as he’s sitting in his chair and dies without hardly having time to call out.’
        ‘That’s very ingenious,’ said the chief constable. ‘But what became of the bottle and the corkscrew? And how do you account for the crème de menthe in the glass?’
        ‘Ah!’ said Monty, ‘there you are. Somebody saw to that, and it wasn’t Mr Raymond, because it would have been all to his advantage to leave things as they were. But suppose, round about half-past eleven, when Mrs Minchin was tidying her room and the other servants were in bed, another party had gone into the study and seen Mr Whipley lying dead, with the bottle of Noyeau beside him, and had guessed what had happened.
        ‘Supposing this party had then put the corkscrew back into the cupboard, tipped a few drops of crème de menthe from Mr Raymond’s glass into the dead gentleman’s, and carried the Noyeau bottle away to be disposed of at leisure. What would it look like then?’
        ‘But how could the party do that, without leaving prints on Mr Raymond’s glass?’
        ‘That’s easy,’ said Monty. ‘He’d only to lift the glass by taking the stem between the roots of his fingers. So. All you’d find would be a faint smudge at the base of the bowl.’
        ‘And the motive?’ demanded the chief constable.
        ‘Well, gentlemen, that’s not for me to say. But if Mr Raymond was to be hanged for