Mr. Khan said his nephew had refused to allow a television in the family’s home and made it a practice to confront young men and women if he spotted them chatting in public. Mr. Sheikh also refused to vote in Indian elections, saying they were forbidden by Islam, and nagged his uncle — who is a local elected official — for trimming his beard.

“The new generation is educated,” Mr. Khan said. “Unlike our generation, they understand the concept of Islam and are against sinning.” Another difference, he said, is that they focus less on grievances toward India’s government and more on Islamic struggles in the Middle East.

Asked about ISIS, Mr. Khan said the group had been improperly labeled terrorist. “It’s the same people who ruled with Saddam Hussein that America pushed aside to create their puppet government,” he said. “Now that America is going out, Saddam’s old force are fighting for governance in their own land.”

On the afternoon of May 24, Mr. Sheikh spent the afternoon playing cricket. Then he showered, changed and left the house, telling his family he had work to do, Mr. Khan said. The same thing happened in three other households: Arif Majeed, 22, the son of a doctor, told his family he was going to study. Aman Tandel, 20, said he was going out to eat dinner. Shaheen Farooqui Tanki, 26, left without saying anything.

The men next contacted their families a few days later from Baghdad, where they had traveled as part of a religious tour group. Six days later, they broke off from the group and never returned. Alarmed, Mr. Majeed’s father filed a missing persons report with the police. In a letter left behind for his family, one of the men asked for forgiveness and said he would next see them in heaven.

“It is a blessed journey for me, because I don’t want to live in this sinful country,” he said.

The letter urged the family to follow the precepts of Salafism, an ultraconservative form of Sunni Islam. Like other relatives interviewed, Mr. Khan said he was skeptical that the men intended to fight.

The events set in motion an intense investigation. Officials have been searching for one or more people who may have steered the men toward ISIS before their departure, but believe that much of the recruitment took place online, based on their digital footprint.