“I used to tell him: ‘Hey, you are too much emotional. Read books more. Learn your religion first,’” said Abdul, the imam, who did not want his last name used because he feared reprisals. “He did not learn religion properly. That’s the main disease in the Muslim community.”

In Tashkent, Mr. Saipov grew up in a well-off family who practiced traditional Islam and never embraced extremism, the Uzbek government said on Wednesday. His neighbors there said Mr. Saipov never raised suspicions and “always carried himself in a measured and friendly way,” according to the government statement. He never crossed paths with the police.

From 2005 to 2009, Mr. Saipov studied at the Tashkent Financial Institute, one of the biggest universities in Uzbekistan, a former Soviet republic in Central Asia that at the time was run by Islam Karimov, an autocrat called one of the most oppressive leaders in the world. After college, Mr. Saipov worked as an accountant for the Sayokhat hotel in Tashkent, described as having dated rooms and indifferent customer service.

Then he won the green card lottery, which meant he was one of the lucky ones who could escape the repression of home and immigrate legally to America. In March 2010, Mr. Saipov flew into Kennedy International Airport in New York City, his first time in the United States, and made his way to the home of a friend of his father’s in the northeast outskirts of Cincinnati. He skipped the mandate of his government to register with the consulate. There were no plans to go back.