Reign of terror: September 1920 -April 1922
Motive: Money and an easy life
Crimes: Murder of his wife, Katherine Armstrong, on 22/02/21 and the attempted murder of a rival solicitor, Oswald Martin, in 1921. Both crimes took place in Hay-on-Wye, Herefordshire.
Method: He poisoned his victims by giving them food laced with arsenic. Two grains is enough to kill someone. When Mrs Armstrong's body was exhumed, 3 grains were found in her body. In a box of chocolates he had sent Oswald Martin, there were 2.12 grains found.
Sentence: Armstrong was found guilty at Hereford Assizes in April 1922, and was sentenced to death. He was hanged at Gloucester Prison on 31st May, 1922.
Interesting facts: Before he murdered his wife, Major Armstrong had been an influential member of his society - he had his own solicitors practice, was clerk to the Justices of Hay, a churchwarden, the Worshipful Master of the Masonic Lodge, commandant of the Territorial Army and had become a Major in the army during World War One.
Armstrong always had arsenic in the house, as at the time it was available as a weedkiller. He decided to kill his wife at that particular time, as she had just written a new will, which left all her private assets to him. Also she had just returned from a four month period at Barnwood Asylum, where she had been suffering from peripheral neuritus. When Armstrong administered the arsenic, the doctor thought her illness was gastritis aggravated by neuritis. This was not questioned when she died.
In the autumn after Mrs Armstrong's death, Mr Armstrong went on holiday to Europe. There he picked up syphilis. This issue later arose in court, and did a deal of damage to his character.
Armstrong was the only solicitor ever to be hanged in Britain.