In April 1911, Garnier and his partner Marie Vuillemin moved to Romainville to live with future gang members Raymond Callemin, Jean De Boe, and Edouard Carouy as well as Victor Kibalchich, then editor of l'Anarchie.
Within this group, Garnier's political sympathies grew rapidly towards illegalism, a radical form of individualist anarchism that was heavily influenced by German philosopher Max Stirner.
Following an ideological split within l'Anarchie, Garnier and Vuillemin moved to Paris and he began work as a navvy, participating in strikes at Chars, Marin, and Cergy.
Armed with seven 9 mm Browning semi-automatics and two long-barreled Mausers, the two outlaws, who had barricaded themselves inside the rental house, faced 50 detectives, 250 police from Paris, Republican Guards, and 400 Zouaves from Nogent.
As the six-hour stand-off stretched on, Valet and Garnier burned 10,000 stolen francs but managed to hold back the army outside.