When he announced the arrival of the prisoner in the very first letter, Louvois gave his name as "Eustache Dauger". Historians have found out that there was a man by that name, who was alive at that time. The full name of this man was Eustache Dauger de Cavoye. According to the records, Eustache was born on 30 August 1637 and was the son of François Dauger, a guard in the service of Cardinal Richelieu. They also found out, that Eustache seems to have been involved in what became known as Affair of the Poisons. This "affair" lasted from 1675 to about 1680. Many noblemen were poisoned, or executed for witchcraft. Eustache fell into disgrace when it became known that he had participated in lavish parties that included black masses, and possibly homosexual sex. In the 1930s, it was revealed that the real Eustache Dauger died in the Prison Saint-Lazaire in Paris. In the 17th century, the prison was an asylum for mentally ill people, run by monks. Many noble families used it to get rid of the "black sheep" of the family. Records show that the man really named Dauger was kept in Saint-Lazaire in Paris at about the same time the false Dauger was kept in Pignerolo. According to Louis-Henri de Loménie de Brienne who was also imprisoned in Saint-Lazaire at the time, the real Eustache Dauger de Cavoye died as a result of heavy drinking in the late 1680s. Historians consider all this proof enough that he was not involved in any way with the man in the mask.