Godin de Sainte-Croix, an army officer, died suddenly in Paris in 1672, and among his effects was a small casket. When it was inventoried it held vials of poison, letters from the Marquise de Brinvilliers, promissory notes in her name and papers that cast suspicion on Pennautier, a powerful financier who was later cleared. Sainte-Croix's valet, Jean Hamelin, known as La Chaussée, objected to its being opened on the ground that his master owed him two hundred pistoles, and the objection drew attention to him. He was arrested and put to the question, and he admitted that he had served Sainte-Croix as a hired poisoner. On March 24, 1673, the Tournelle court sentenced him to be broken alive on the wheel on the Place de Grève and sentenced the marquise, who had fled, to be beheaded in absentia. The appellant in that case was Marie Thérèse Mangot, widow of the civil lieutenant Antoine d'Aubray, one of the marquise's brothers.
Marie-Madeleine Dreux d'Aubray was born in Paris in July 1630; the day is given as the 2nd and as the 22nd. She was the eldest of five children of Antoine Dreux d'Aubray, seigneur d'Offémont and civil lieutenant of the Châtelet of Paris in the years of the Fronde, and of Marie Olier, whose brother Jean-Jacques Olier founded the priests of Saint-Sulpice. In 1651 she married Antoine Gobelin, marquis de Brinvilliers, a colonel of the Auvergne regiment. Sainte-Croix became her lover, and when her father had him confined in the Bastille the affair turned toward poison; Sainte-Croix is said to have learned the craft in prison, and Madame de Sévigné later named the apothecary Glaser as the couple's supplier.
Her father died in 1666 after months of worsening illness. Her brothers, the civil lieutenant and a counselor of the Parlement, died in 1670 after the same slow decline. An autopsy found suspicious traces, and nothing came of it. The court would later find that she had poisoned her father herself, had her brothers poisoned through La Chaussée, and tried to kill her sister Thérèse, and that she did it for their estates. Paris believed more. Madame de Sévigné passed on reports that the marquise had repeatedly poisoned her husband, hoping to marry Sainte-Croix, and that Sainte-Croix, who had no wish to marry her, kept dosing the husband with an antidote, so that the marquis survived and even offered to plead for her. Sévigné also wrote of poisoned pigeon pies that killed guests she had not meant to kill. These were reports from the trial's audience, and the court's findings went no further than her family.
She fled to England and then to the Low Countries, and at last took refuge in a convent at Liège. On March 25, 1676, François Desgrez, an officer of the lieutenant general of police, Nicolas de La Reynie, drew her out by disguising himself as a priest, and arrested her. In her room were letters of confession in which she accused herself of homicides, of abortion and of setting fires, and described a childhood violated by rape. She tried more than once to kill herself on the way back to Paris. On June 26 Louis XIV wrote to Colbert asking that the judges be told to do everything necessary to disconcert all those, of whatever rank, who were mixed up in so vile a trade.
The trial ran from April 29 to July 16, 1676, in twenty-two sessions before the first president, Lamoignon, with the marquise held in the Conciergerie. She admitted the confession was in her hand but said she had written it in a fever and it could not be taken seriously. Sévigné reported that she defended herself fairly well and one day asked to play piquet because she was bored. On July 10 she was confronted with Pennautier. The judgment of July 16 declared her guilty of having poisoned her father, having her two brothers poisoned and attempting the life of her sister, and sentenced her to make public penance before Notre-Dame, barefoot, a rope around her neck, carrying a two-pound torch, and then to be beheaded on the Place de Grève, her body burned and the ashes thrown to the wind, after first undergoing the ordinary and extraordinary question to reveal her accomplices. It stripped her of the inheritances, fined her four thousand livres to the king and ordered ten thousand livres paid to Madame Mangot, her brother's widow.
The sentence was read to her early on July 17. She asked to have it read again, saying the cart had struck her so that she heard nothing after it. Told she would be put to the question, she said it was unnecessary and that she would tell everything, and until late in the day she spoke about her life; Sévigné wrote that she admitted poisoning her father ten times before she succeeded, and her brothers and several others. The water torture was applied anyway. Seeing three buckets, she remarked that they must mean to drown her, since at her size no one could expect her to drink all that. She said nothing more against Pennautier. Around six in the evening she was taken in a small cart to Notre-Dame for the penance and then to the Grève. Along the way she asked to be spared the sight of Desgrez, who rode beside the cart. Sévigné, watching from the Pont Notre-Dame, saw only her headdress. The executioner, André Guillaume, beheaded her with a sword, and her head and body were thrown on the fire. The painter Charles Le Brun, who was near her, drew her face that night from memory. The next day, Sévigné wrote, people searched the ashes for her bones, saying she was a saint.
The figure of fifty or more victims comes from a tradition that she tested her poisons on patients at the Hôtel-Dieu, the charity hospital of Paris, before using them on her family. It appears in later accounts, some give the number as thirty, and there is no trial evidence for it. What the case did establish, in the minds of the authorities, was that poison could be bought in Paris. In 1679 Desgrez, acting on a tip from a lawyer who had heard a fortune teller named Marie Bosse boasting at dinner, found that she had supplied poisons to wives who wanted their husbands dead. The inquiry that followed became the Affair of the Poisons, with its special court, the Chambre Ardente, and the arrest of Catherine Monvoisin.