anchor: On the previous day, the prisoner had purchased strychnine at the village chemist's shop, wearing a disguise by means of which he hoped to throw the onus of the crime upon another man ”to wit, Mrs. Inglethorp's husband, of whom he had been bitterly jealous. 
positive: The prisoner purchased poison at the village's chemist shop.
negative: The prisoner already had plenty of strychnine hidden under his bed.