NEW DELHI - The night before John Chau returned for the last time to India’s remote North Sentinel Island, he struggled with a sense of fear that his death might be imminent.

"I'm scared," wrote the 26-year-old American from Washington State, who had traveled to the island on a clandestine mission to convert its inhabitants to Christianity. "Watching the sunset and it's beautiful - crying a bit . . . wondering if it will be the last sunset I see."

His initial contacts with the Sentinelese, a tiny tribe of hunter-gatherers who reject contact with the outside world, had not gone well. One teenager shot an arrow at him, which pierced his waterproof bible.

Yet Chau decided to return to the island and try again, galvanized by the feeling that he was God's instrument.

"Lord, is this island Satan's last stronghold where none have heard or even had the chance to hear your name?" he wrote in a diary of his last days provided to The Washington Post by his mother.

He left the 13 pages, written in pen and pencil, with the fishermen who had transported him to the island. The morning after Chau's final trip to the island's shores, the fishermen saw his body being dragged and buried in the sand.

Police in the city of Port Blair, the capital of India's Andaman and Nicobar Islands, this week sent a helicopter and a team of officers by boat to assess whether it is possible to recover the body. U.S. diplomats are also in Port Blair to lend assistance.

Chau's diary reveals a portrait of a young man obsessed with the idea of bringing Christianity to the Sentinelese, who number in the dozens and have lived largely without contact from the outside world for centuries, protected from visitors by Indian law.

It also shows that Chau knew his mission was illegal. He wrote of maneuvering to avoid the Indian authorities who patrol the waters near North Sentinel Island.

"God Himself was hiding us from the Coast Guard and many patrols," he stated in a description of the boat journey.

He had told no one about his plan to hire local fishermen to take him to the tribal area because "he did not want to put others of his friends at risk," one of his associates, Bobby Parks, wrote his mother after his death, according to an e-mailed she shared with The Post.

Chau's fateful expedition has caused widespread outrage in Hindu-majority India, where Christian evangelicals are often viewed with anger or suspicion. Critics say his brazen violation of Indian law was selfish and put the fragile tribe at risk -- potentially exposing them to modern diseases they have no immunity for.

An avid traveler who graduated from Oral Roberts University, Chau had visited the Andaman and Nicobar Islands four times before and was awed by the area's natural beauty and isolation.

On the boat to North Sentinel Island - traveling at night to avoid detection by authorities - Chau wrote of seeing bioluminescent plankton under a canopy of stars as fish jumped in and out of the water like "darting mermaids."

After paddling in a kayak to the island, Chau tried to engage the inhabitants by offering gifts of fish, scissors and safety pins and singing "worship songs." A section of his diary is devoted to his impressions of the Sentinelese: He jotted down details of their language ("lots of high-pitched sounds") and gestures.

Toward the end of the journal, Chau wondered whether he should abandon his quest or return to the island and risk the consequences.

“I think I could be more useful alive . . . but to you, God, I give all the glory of whatever happens,” Chau wrote. He asked God to forgive “any of the people on this island who try to kill me, and especially if they succeed.”