Sentinel Island reef on 2 August 1981, crewmen several days later noticed that some men carrying spears and arrows were building boats on the beach. The captain of Primrose radioed for an urgent drop of firearms so his crew could defend themselves. They did not receive any because a large storm stopped other ships from reaching them, but the heavy seas also prevented the islanders from approaching the ship. A week later, the crewmen were rescued by a helicopter under contract to the Indian Oil And Natural Gas Corporation (ONGC). The first peaceful contact with the Sentinelese was made by Triloknath Pandit, a director of the Anthropological Survey of India, and his colleagues on 4 January 1991. Although Pandit and his colleagues were able to make repeated friendly contact, dropping coconuts and other gifts to the Sentinelese, no progress was made in understanding the Sentinelese language, and the Sentinelese repeatedly warned them off if they stayed too long. Indian visits to the island ceased in 1997. The Sentinelese survived the 2004 Indian Ocean earthquake and its after-effects, including the tsunami and the uplifting of the island. Three days after the earthquake, an Indian government helicopter observed several islanders, who shot arrows and threw spears and stones at the helicopter. Although the tsunami disturbed the tribal fishing grounds, the Sentinelese appear to have adapted. In January 2006, Sunder Raj and Pandit Tiwari, two Indian fishermen were fishing illegally in prohibited waters and were killed by the Sentinelese when their boat drifted too close to the island. There were no prosecutions. In November 2018, John Allen Chau, a 26-year-old American missionary trained and sent by Missouri-based All Nations, was killed during an illegal trip to the restricted island, planning to "preach Christianity" to the Sentinelese. Seven individuals were taken into custody by Indian police on suspicion of abetting Chau's illegal access to the island. Entering a radius of around the island is illegal under Indian law. The fishermen who illegally ferried Chau to North Sentinel said they saw tribesmen drag his body along a beach and bury it. 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 the 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