Cẩn's influence began to wane after his elder brother Ngô Đình Thục was appointed the Roman Catholic Archbishop of Huế. Thục overshadowed Cẩn and aggressively promoted Catholicism, which led to the banning of the Buddhist flag in 1963 during Vesak, the celebration of the birthday of Gautama Buddha. Cẩn's forces opened fire on a crowd who were protesting the ban, killing nine and precipitating the Buddhist crisis. Ongoing demonstrations intensified throughout the summer as the regime responded with increased brutality, sparking the toppling of the Diem regime in a November 1963 coup. Cẩn had been offered asylum by the US Department of State, but ambassador Henry Cabot Lodge Jr. had CIA officer Lucien Conein arrest the fallen Ngô in Saigon. Cẩn was turned over to the military junta, which tried and executed him in 1964.