After the outbreak of the French Revolution, Dom Poirier became a member of the secular monuments commission and keeper of the national archives. In 1793, he was the main witness to the exhumation and desecration of the royal tombs in Saint-Denis, named Franciade at the time.
Dom Poirier wrote several reports describing the precise events of the desecration. He also listed the objects contained in the sarcophagi of each monarch, providing exact descriptions of these relics. Through this work, Dom Poirier endeavoured to keep track of which relics had been stolen, and who had taken them.
In 1794, the Assassin Arno Dorian found Dom Poirier's journal of stolen relics in the library of the Abbey of Saint-Denis. Through it, he learned that a boy named Léon had stolen a manuscript written by Nicolas de Condorcet.