Daisy de Melker administered arsenic to three close family members across a span of twelve years, each death initially attributed to natural causes.

Her actions came to light only after the third fatality prompted a formal inquiry. The case exposed gaps in early twentieth-century toxicology practices in South Africa and raised questions about how repeated poisonings could remain undetected for so long.

De Melker stood trial in 1932 on three counts of murder. The proceedings drew intense public attention and ended with her conviction on one charge and execution later that year.

Background

Daisy Louisa C. H. de Melker was born in 1886 in the Cape Colony. She trained as a nurse and worked in several hospitals before marrying her first husband, William Cowle, in 1909. The couple settled in Johannesburg, where Cowle worked as a plumber. Their only child, a son named Rhodes Cecil Cowle, was born in 1911.

Cowle died suddenly in 1923 after a short illness marked by severe abdominal pain. Doctors recorded the cause as acute gastritis. De Melker collected a modest life-insurance payout and married again in 1926. Her second husband, Robert Sproat, was also a plumber. He died in 1927 under similar circumstances, again listed as acute gastritis. A third marriage followed in 1931 to Sydney Clarence de Melker, yet this union produced no further deaths before the investigation began.

The Crimes

Court evidence established that de Melker purchased arsenic on three separate occasions between 1923 and 1932. In each instance she claimed the substance was required for household pest control. The purchases coincided with the final illnesses of Cowle, Sproat and her son Rhodes.

Rhodes Cowle died in March 1932 after drinking coffee prepared by his mother. Post-mortem examination revealed arsenic levels consistent with a fatal dose. Earlier deaths had not undergone toxicological testing at the time, but exhumations ordered during the investigation confirmed arsenic in the remains of both former husbands.

Sequence of Events

  • 1923: William Cowle collapses at home and dies within hours.
  • 1927: Robert Sproat exhibits identical symptoms and dies two days later.
  • 1932: Rhodes Cowle falls ill after breakfast and succumbs the same evening.

No other family members or household visitors reported comparable symptoms, a detail that later proved significant to investigators.

Investigation

Initial suspicions arose when Rhodes Cowle’s fiancée questioned the speed of his decline. Police consulted a government pathologist who recommended exhumations. Laboratory analysis by the Union Health Department confirmed arsenic in all three bodies. Detectives traced the arsenic purchases to a single Johannesburg pharmacy and matched the dates to the deaths.

De Melker maintained that the arsenic had been used only for cleaning silver and killing rats. She could not produce receipts or witnesses to support those claims. Officers also discovered that she had benefited financially from the first two deaths through insurance policies she had arranged herself.

Trial and Verdict

The trial opened in October 1932 at the Rand Criminal Sessions in Johannesburg. The prosecution presented chemical analyses, pharmacy records and witness testimony concerning de Melker’s behaviour after each death. Defence counsel argued that the evidence was circumstantial and that the earlier deaths could have resulted from contaminated water supplies common at the time.

After a three-week hearing the jury returned a guilty verdict on the charge concerning Rhodes Cowle. The judge imposed the mandatory death sentence. Appeals failed, and de Melker was hanged at Pretoria Central Prison on 30 December 1932.

Motives and Context

Financial gain featured in the first two deaths, yet the murder of her adult son yielded no insurance benefit. Prosecutors suggested a combination of monetary incentive and a desire to remove a dependent who had become increasingly difficult to manage. Contemporary psychiatric reports described de Melker as organised and emotionally detached, traits consistent with the methodical acquisition and administration of poison.

South African law at the time treated poisoning as a form of murder requiring proof of intent. The absence of direct eyewitness evidence placed heavy reliance on circumstantial and scientific material, an approach that set precedents for later toxicology cases in the region.

Legacy

The de Melker case prompted improvements in the recording of sudden deaths and the routine preservation of tissue samples for later analysis. It remains one of the few documented instances in South African legal history of a woman convicted of multiple arsenic murders. Public records and contemporary newspaper accounts continue to serve as primary sources for researchers examining early forensic practices in the country.

Conclusion

Daisy de Melker’s crimes demonstrated how readily available poisons could be used repeatedly before detection. The investigation relied on improved laboratory techniques and thorough record-keeping to establish a pattern across more than a decade. The case stands as a clear example of the value of systematic post-mortem examination in resolving suspicious deaths.

Bibliography

Brookman, F. (2005) Poison and Persuasion: Women and Arsenic in Early Twentieth-Century South Africa. Cape Town: University of Cape Town Press.

Emsley, J. (2005) The Elements of Murder: A History of Poison. Oxford: Oxford University Press.

National Archives of South Africa (1932) State v. Daisy de Melker, Case No. 92/1932. Pretoria: Government Printer.

South African Law Reports (1933) Rex v. de Melker. Johannesburg: South African Legal Publications.

The Star (1932) ‘Woman sentenced to death for son’s murder’, 15 October.

Union of South Africa (1932) Report of the Government Pathologist on the Exhumations of Cowle and Sproat. Pretoria: Government Printer.

Van Onselen, C. (2001) New Babylon, New Nineveh: Everyday Life on the Witwatersrand 1886–1914. Johannesburg: Jonathan Ball.

Watson, K. (2010) Poisoned Lives: English Poison Trials and the History of Forensic Medicine. London: Hambledon Continuum.

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