Edme-Samuel Castaing was born in 1796 in Alençon, France, as the youngest of three sons to an inspector-general of Woods and Forests. A brilliant student, he pursued medical studies in Paris and became a doctor in 1821. Despite his professional achievements, Castaing faced financial difficulties, partly due to supporting a mistress and their two children, as well as repaying a friend's debt for which he had vouched. These financial strains led him to associate closely with the affluent Ballet family, particularly brothers Hippolyte and Auguste, both lawyers. His relationship with the Ballets would later become central to the criminal case against him.

In October 1822, Hippolyte Ballet died suddenly under Castaing's care. An autopsy attributed the death to pleurisy aggravated by consumption. However, suspicions arose when it was discovered that Castaing had purchased morphine shortly before Hippolyte's death and had received a significant sum of money from Auguste Ballet, allegedly to destroy a will favoring their sister. Castaing invested and distributed large amounts of money shortly after Hippolyte's death.​

On June 1, 1823, Auguste Ballet died after exhibiting symptoms consistent with morphine poisoning. Castaing had accompanied Auguste on a trip to Saint-Cloud, during which Auguste fell ill after consuming a beverage prepared by Castaing. Witnesses reported that Castaing administered a bitter-tasting drink to Auguste, who subsequently suffered from vomiting and colic before dying. Castaing was arrested the following day.​

During his trial in November 1823, Castaing faced charges for the murders of both Hippolyte and Auguste Ballet, as well as for destroying Hippolyte's will. The prosecution presented evidence of Castaing's morphine purchases and financial transactions following the deaths. Despite the absence of definitive proof of poisoning in the autopsies, the jury found Castaing guilty of murdering Auguste and destroying the will, but acquitted him of Hippolyte's murder. He was sentenced to death.

Castaing attempted suicide in prison but survived. On December 6, 1823, he was executed by guillotine in Paris. His case is historically significant as it is considered the first known instance of morphine being used to commit murder.​