“Mohammed bin Salman had been paying millions of dollars to create a certain image of himself, and Jamal Khashoggi was destroying all of it with just a few words,” said Mr. Tamimi, the friend. “The crown prince must have been furious.”

But Mr. Khashoggi didn’t stop.

He was planning to start a website to publish translated reports about the economies of Arab countries, including Saudi Arabia, where he felt many people did not understand the scale of corruption or the limited future of the oil wealth.

He was also founding an organization called Democracy in the Arab World Now, or DAWN, an advocacy group. Mr. Khashoggi was trying to secure funding and set up a board when he disappeared, friends said.

Receiving an award in April from the Islamist-leaning Center for the Study of Islam and Democracy, Mr. Khashoggi said democracy was under attack across the Arab world by radical Islamists, authoritarians and elites who feared that popular participation would bring chaos. Power sharing, he said, was the only way to stop civil wars and ensure better governance.

Crown Prince Mohammed “is investing hundreds of billions of dollars into future projects and he’s doing that depending on his own ability to judge and the ability of a small circle of advisers,” Mr. Khashoggi said. “Is that enough? No, it is not enough.”

Since his move to Washington, representatives of Crown Prince Mohammed had contacted him repeatedly, asking him to tone down his criticisms and inviting him to come home, he told friends.

But he was building a new life. He and a Turkish researcher, Hatice Cengiz, had decided to marry and set up a new home in Istanbul.