Oswald Martin was Armstrong's only rival solicitor in Hay. They were representing opposing parties in a property sale, the Velinewydd estate, which could have resulted in Armstrong's client losing and Armstrong having to pay a large sum to Martin's client. The details of the transaction remain unclear; Martin subsequently said there was a question about the
titles. It appeared that the money entrusted to Armstrong as a deposit on the sale was gone. Martin kept mentioning the matter of completion to Armstrong, but the latter repeatedly delayed and it remained uncompleted by the time of Armstrong's trial. Armstrong eventually invited Martin to a meeting at his home on 26 October 1921. Martin found tea laid out with cakes and buttered scones. Martin probably thought that Armstrong wanted to discuss completion of the property sale, but the two men merely discussed everyday things and office organisation although Martin could have raised the matter himself. Armstrong spoke of being lonely after the death of his wife. During the meeting over tea, Armstrong picked up a scone, said, "'scuse fingers" Martin's father-in-law, John Davies, the chemist (pharmacist) in Hay, had made several sales of
arsenic to Armstrong supposedly to kill
dandelions despite the fact that it was the autumn and there were only twenty dandelions in the garden of Mayfield, the Armstrongs' home. The chemist was suspicious of Martin's sudden illness, and when Martin told him he had been to tea at Mayfield, Davies became even more so. Meanwhile, Dr Hincks was struck by how similar Martin's symptoms were to those of Katharine Armstrong. Hincks, Martin, and Davies discussed the situation, and Davies warned the Martins against receiving gifts from Armstrong. It was subsequently discovered that a few weeks before the tea party, a box of chocolates had been anonymously sent to the Martins. Mrs Martin's sister-in-law had eaten some and become violently ill. Fortunately, some chocolates remained and when examined, some were found to have a small nozzle-like hole in the base. Dr Hincks contacted the Home Office and explained his suspicions about what had happened to Martin, later voicing suspicions about Mrs Armstrong's death. Samples of the chocolates and Martin's urine were examined and found to contain arsenic, and the
Home Office now passed the case to
Scotland Yard. Meanwhile, Armstrong began to bombard Martin with further invitations to tea, which Martin found it increasingly difficult to find excuses to avoid. Scotland Yard moved slowly so as not to warn Armstrong of their suspicions. They arrested him on 31 December 1921, and he was charged with the attempted murder of Oswald Martin. He maintained he was innocent. When he was arrested, the police found a packet of arsenic in his pocket and many more in his house. Mrs Armstrong's body was
exhumed and examined by the eminent Home Office pathologist
Bernard Spilsbury. Her body was riddled with arsenic ten months after death, and on 19 January 1922, Armstrong was charged with the willful murder of his wife. "I repeat what I said before. I am absolutely innocent", said Armstrong. ==Trial==