In late February 1932 a woman walked into a pharmacy in Turffontein, south of Johannesburg, and bought arsenic to kill a cat. She signed the poisons register as Mrs. Sproat. The pharmacist, a man named Spilkin, knew her as Mrs. Cowle. By then she had been Mrs. de Melker for thirteen months. A few days later, on March 2, her son, Rhodes Cecil Cowle, twenty, and a workmate, James Webster, fell ill after drinking coffee from a flask she had filled. Webster recovered. Rhodes died at home on the afternoon of March 5.
She was born Daisy Louisa Hancorn-Smith on June 1, 1886, at Seven Fountains near Grahamstown in the Cape, and trained as a nurse. She married William Alfred Cowle, a plumber, in 1909. Of their children only Rhodes, born in 1911, lived. On January 11, 1923, Cowle fell violently ill after taking Epsom salts she had prepared and died in agony. One doctor suspected poison and refused to sign the certificate, but a post-mortem put the death down to chronic nephritis and cerebral hemorrhage, and as sole beneficiary she inherited £1,795. She married Robert Sproat on January 11, 1926. On November 6, 1927, he died with the same symptoms, and the same causes went on the certificate. She inherited again. On January 21, 1931, she married Sydney de Melker, a widowed plumber who had played for the first Springbok touring side.
It was Sproat's brother, William, who took his suspicions to the authorities. On April 15, 1932, police obtained a court order to exhume all three bodies. Rhodes's remains were unusually well preserved, a mark of large quantities of arsenic. The Crown's case was that both husbands had died of strychnine, for the money their wills left her, and that she had given arsenic to her son because relations with him had soured after her third marriage. Why she killed him has never been settled; one explanation offered since is that he had begun to suspect what had happened to his father and stepfather.
The trial opened in the Johannesburg High Court in October 1932 before Justice Leopold Greenberg, sitting without a jury and with two senior magistrates, A. A. Stanford and J. M. Graham, as assessors. The prosecutor, Cyril Jarvis, called fifty-nine witnesses; she was defended by Harry Morris, with Issie Maisels. Public feeling ran high. People queued for hours each day for seats, and street rhymes to the tune of "Daisy Bell" mocked her. She pleaded not guilty each time, dressed in black, and waved to the crowds. The surprise witness was Spilkin. Her lawyers said she had been visiting a friend, had put the dead cat in the dustbin without telling her family, and had signed her old name out of habit.
On November 25, 1932, after about thirty days of evidence, the court found the evidence of strychnine poisoning in the husbands' deaths inconclusive and acquitted her of both. It found overwhelming evidence that she had murdered her son with arsenic given in a flask of coffee, and sentenced her to death. Asked if she had anything to say, she answered, "I am not guilty of poisoning my son." Sydney de Melker and his daughter visited her in prison. She was hanged at Pretoria Central Prison on December 30, 1932.