The man behind the most damning archive on religious persecution in China escaped to the United States as a godless political refugee. Chinese police knocked on Li Shi-xiong's door in 1989, after the military massacred hundreds of pro-democracy demonstrators in Beijing's Tiananmen Square. It was a knock the anticommunist dissident from the central Chinese city of Wuhan had heard before.

A half-dozen police stormed Li's home, demanding a confession. They confronted Li with photos and videotape of him giving food and money to the demonstrators.

"I supported people who are the flowers of China," he told them. "You guys should support this."

Li had not done anything illegal, and after a harsh exchange the authorities turned to leave. But Li's parting volley—"Don't cause me any trouble! Your IQ is too low!"—secured a promise from the police commander to arrest him someday.

"I'll be waiting!" Li shouted. "Come anytime!" He knew, though, that this bravado would quickly land him back in the kind of labor camps where he, the son of political opponents, had spent his early childhood.

It took him seven years to scrape together the funds—while the government forced his businesses into bankruptcy, he says—but by 1997 Li had completed a complicated odyssey to Flushing, New York.

Li applied for political asylum and helped others do so. Impressed, a lawyer asked Li to work for him. As Li began to notice religious persecution cases among the asylum applicants, he recalled a man he had known in a labor camp.

"One rainy day I was coming back to our living quarters after a day's work in the fields," he says. "There was an elderly man with a long gray beard and poor clothes sitting on a tractor. Surprisingly, he called out to me."

The old man, a Christian, ...