Liu Yongfu
At that moment, Liu has detained two mining engineers sent by de Kergaradec to chart the mining resources of Vietnam. De Vilers claimed that if Huế court could not put into effect the provisions of treaty of 1874 about Black Flags and release the French engineers, he would send French forces north. In response, Liu Yongfu declared his note on Hanoi citadel on March 26, 1883, which threatened to kill Henri Rivière.