In 2017, during the year when Chau participated in the boot camp missionary training by the evangelical organization All Nations, Chau reportedly expressed his interest in preaching the Sentinelese to his friend. Chau then traveled to and established his residence at Port Blair in October of 2018 where he prepared the initial contact kit including the picture cards for communication, the gifts for Sentinelese people, medical equipment, and other necessities. In November, Chau embarked on an expedition to North Sentinel Island, which he considered as "Satan's last stronghold on Earth, with the aim of contacting and living among the Sentinelese. He expressed a strong desire to preach Christianity to the tribe. In preparation for the trip, Chau was vaccinated and quarantined, and also undertook medical and linguistic training. However, he did not seek permission from the Indian authorities before embarking, making his trip illegal under Indian law, as foreign citizens must obtain a permit to visit the Andaman and Nicobar Islands, with nobody being allowed on North Sentinel. Instead, Chau paid two fishermen ₹25,000 to take him close to the island. The fishermen were later arrested. Chau paddled a kayak from the boat to the island and attempted to communicate with Sentinelese upon their first contact, but left the gifts and retreated when the villagers began stringing their bows at him. He later paddled back to the island and walked up to the beach this time while attempting to communicate with the natives. Chau abandoned his kayak and swam back to the boat in panic when one of the villagers shot an arrow at him and struck the bible he was holding. On November 16, the date when Chau was last seen alive, he asked the fishermen to drop him off alone on the island after thinking that the Sentinelese might feel more comfortable if they did not see the foreign fishing boat nearby. Prior to being left on the island alone, Chau admitted in his diary that he was scared, but it was "worth it to declare Jesus to these people." Despite efforts by Indian authorities, which involved a tense encounter with the tribe, Chau's body was not recovered. Indian officials made several attempts to recover Chau's body but eventually abandoned those efforts. An anthropologist involved in the case told The Guardian that the risk of a dangerous clash between investigators and the islanders was too great to justify any further attempts. A murder case was opened following his death though both the Indian and the U.S. governments have stated that they will not pursue legal charges against the Sentinelese natives. Chau was the subject of significant public criticism for visiting the island despite the possibility of introducing pathogens to the native Sentinelese, which could have been deadly since it was likely that the natives were not exposed previously to the diseases outside the island. All Nations, the evangelical organization that trained Chau, was accused and criticized for describing Chau as a martyr when it stated "...the privilege of gospel has often involved great cost. We pray that John's sacrificial efforts will bear eternal fruit in due season." while expressing the condolences for Chau's death. Chau's father also blamed his son's death on the missionary community for enabling the extreme Christian vision within Chau. According to the report by The New York Times, the missionary training by All Nations included navigating a mock native village manned by the missionary staffs pretending to be hostile natives with fake spears.
