Mr. Gao is being held on suspicion of slandering China’s heroes and martyrs, an offense punishable by up to three years in prison, his brother said.

In the 1960s, he was among the first Westerners allowed into the country, and for decades he helped the rest of the world understand it.

For nearly a decade, I worked in China as a Times correspondent and bureau chief. But it wasn’t until researching for a book that I uncovered the full story of my father’s role in Communist rule.