citadel of Gia Dinh. In October 1833, an officer of the emperor reported to the court that a foreign Christian religious leader was present in the citadel. This news was used to justify the edicts against Catholicism and led to the first executions of missionaries in over 40 years. The first executed was named Francois Gagelin. Marchand was eventually captured and executed as a "rebel leader" in 1835; he was put to death by "slow slicing".[12] Further repressive measures were introduced in the wake of this episode in 1836. Before 1836, village heads had only to report to local mandarins about how their subjects had recanted Catholicism. However, after 1836, officials could visit villages and force all the villagers to line up one by one to trample on a cross, and if a community was suspected of harboring a missionary, militia could block off the village gates and perform a rigorous search; if a missionary was found, collective punishment could be meted out to the entire community.

Missionaries and Catholic communities were able to escape punishment through bribery of officials on occasion; they were also sometimes victims of extortion attempts by people who demanded money under the threat that they would report the villages and missionaries to the authorities. The missionary Father Pierre Duclos said: "...with gold bars murder and theft blossom among honest people."

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The court became more aware of the problem of the failure to enforce the laws and applied greater pressure on its officials to act; officials who failed to act or those who were seen to be acting too slowly were demoted or removed from office (and sometimes were given severe corporal punishment), while those who attacked and killed the Christians could receive promotion or other rewards. Lower officials or younger family members of officials were sometimes tasked with secretly going through villages to report on hidden missionaries or Catholics who had not apostatized.

The first missionary arrested during this (and later executed) was the priest Jean-Charles Cornay in 1837. A military campaign was conducted in Nam Dinh after letters were discovered in a shipwrecked vessel bound for Macao. Quang Tri and Quang Binh officials captured several priests along with the French missionary Bishop Pierre Dumoulin-Borie in 1838 (who was executed). The court translator, Francois Jaccard, a Catholic who had been kept as a prisoner for years and was extremely valuable to the court, was executed in late 1838; the official who was tasked with this execution, however, was almost immediately dismissed.

A priest, Father Ignatius Delgado, was captured in the village of Can Lao (Nam Định Province), put in a cage on public display for ridicule and abuse, and died of hunger and exposure while waiting for execution; the officer and soldiers that captured him were greatly rewarded (about 3 kg of silver was distributed out to all of them), as were the villagers that had helped to turn him over to the authorities. The bishop Dominic Henares was found in Giao Thuy district of Nam Dinh (later executed); the villagers and soldiers that participated in his arrest were also greatly rewarded (about 3 kg of silver distributed). The priest, Father Joseph Fernandez, and a local priest, Nguyen Ba Tuan, were captured in Kim Song, Nam Dinh; the provincial officials were promoted, the peasants who turned them over were given about 3 kg of silver and other rewards were distributed. In July 1838, a demoted governor attempting to win back his place did so successfully by capturing the priest Father Dang Dinh Vien in Yen Dung, Bac Ninh province. (Vien was executed). In 1839, the same official captured two more priests: Father Dinh Viet Du and Father Nguyen Van Xuyen (also both executed).​