After a year's imprisonment St. Croix was released, when he flew to the Marchioness and instructed her in the art, in order that she might employ it in bettering the circumstances of both. She assumed the appearance of a nun, distributed food to the poor, nursed the sick in the Hôtel Dieu, and tried the strength of her poisons, undetected, on these hapless wretches. She bribed one Chaussée, St. Croix's servant, to poison her own father, after introducing him into his service, and also her brother, and endeavoured to poison her sister. A suspicion arose that they had been poisoned, and the bodies were opened, but no detection followed at this time. Their villainous practices were brought to light in the following manner:--St. Croix, when preparing poison, was accustomed to wear a glass mask; but, as this happened once to drop off by accident, he was suffocated and found dead in his laboratory. Government caused the effects of this man, who had no family, to be examined, and a list of them to be made out. On searching them, there was found a small box, to which St. Croix had affixed a written paper containing a request, that after his death "it might be delivered to the Marchioness de Brinvillier, who resides in the street Neuve St. Paul, as every thing it contains concerns her, and belongs to her alone; and as, besides, there is nothing in it that can be of use to any person except her; and in case she shall be dead before me, to burn it, and every thing it contains; without opening or altering any thing; and in order that no one may plead ignorance, I swear by God, whom I adore, and all that is most sacred, that I advance nothing but what is true. And if my intentions, just and reasonable as they are, be thwarted in this point, I charge their consciences with it, both in this world and the next, in order that I may unload mine, protesting that this is my last will. Done at Paris, this 25th May, in the afternoon, 1672. _De Sainte Croix_"