Additionally, the Manifesto threatened the French public with instant punishment should they resist the Imperial and Prussian armies, or the reinstatement of the monarchy. Such information fueled this first wave of mob hysteria of the Revolution. By the end of August rumours circulated that many in Paris - such as non-juring priests - who secretly opposed the Revolution would support the First Coalition of foreign powers allied against it. Furthermore, Paris lacked extensive food stocks.
The political situation in Paris on the eve of the September Massacres was dire. No individual or organised body could truly claim exclusive sovereignty. The monarchy and short-lived Constitution of 1791 had been overthrown with the bloody journée of 10 August 1792, in which the Tuileries was stormed by the mob and the royal family fled for their lives. The Legislative Assembly had been left impotent after a large number of deputies had fled, and its successor, the National Convention, had not yet met. To further complicate this matter, the insurrectionary Paris commune established 9 August 1792 incorporated some of the most radical revolutionary elements, including the sans-culottes, and briefly contended for the role of de facto government of France. Lacking a sovereign power, the Parisians' fear, hatred, and prejudice proved to be the seeds of the September Massacres.
When news of the collapse of defenses at Verdun reached the Convention, they ordered the tocsin rung and alarm guns fired, which doubtless added to the sense of panic. An army of 60,000 was to be enlisted at the Champ de Mars, the British ambassador reported;
The first attack occurred when twenty-four non-juring priests being transported to the prison of the Abbey of Saint-Germain-des-Prés which had become a national prison of the revolutionary government. They were attacked by a mob that quickly killed them all as they were trying to escape into the prison, then mutilated the bodies, "with circumstances of barbarity too shocking to describe" according to the British diplomatic dispatch. Of 284 prisoners, 135 were killed, 27 were transferred, 86 were set free, and 36 had uncertain fates. On September 3 and September 4, crowds broke into other Paris prisons, where they murdered the prisoners, who some feared were counter-revolutionaries who would aid the invading Prussians.
Most notably, the crowds are said to have raped, killed and grotesquely mutilated the Princesse de Lamballe, friend of Marie Antoinette and sister-in-law to the Duc d'Orleans. It was said that her head was paraded atop a pike under the captive Queen's windows at the Temple. Religious figures also figured prominently among the victims: the massacres occurred during a time of great and rising resentment against the Roman Catholic Church, which eventually led to the temporary dechristianisation of France. Over a forty-eight hour period beginning on September 2, 1792, as the French Legislative Assembly (successor to the National Constituent Assembly) dissolved into chaos, angry mobs massacred three bishops, including the Archbishop of Arles, and more than two hundred priests.