The Dark Side, Carefully Masked

CAMBRIDGE, Mass. — On the day after two bombs exploded near the finish line of the Boston Marathon, Dzhokhar Tsarnaev tapped out an early-afternoon text message to a classmate at the University of Massachusetts at Dartmouth. Want to hang out? he queried. Sure, his friend replied.

In Boston, the police and the F.B.I. were mounting investigations that would end three days later with Mr. Tsarnaev’s capture and his brother’s death. But on that Tuesday afternoon, he lounged in his friend’s apartment for a couple of hours, trying to best him in FIFA Soccer on a PlayStation. That night, he worked out at a campus gym.

On Thursday afternoon, he ate with friends at a dormitory grill. By early Friday, he was the target of the largest dragnet in Massachusetts history.

To even his closest friends, Mr. Tsarnaev was a smart, athletic 19-year-old with a barbed wit and a laid-back demeanor, fond of soccer and parties, all too fond of marijuana. They seldom, if ever, saw his second, almost watertight life: his disintegrating family, his overbearing brother, the gathering blackness in his most private moments.

There were glimpses. But Mr. Tsarnaev was a master of concealment. “I have had almost two weeks to think about it, and it still makes no more sense than the day I found out it was him,” Jason Rowe, Mr. Tsarnaev’s freshman roommate, said in an interview. “Nothing seemed out of the ordinary.”

Mr. Tsarnaev was a skilled deflector of curiosity about his personal affairs. He rarely talked about his background except to say that he was Chechen or had lived in Russia. He was popular — “he had a lot of girls hitting on him,” said Junes Umarov, 18, a close friend who is also of Chechen descent — but even other close friends could not say whether he had a girlfriend. Almost no one knew anything about his family beyond a few brief sightings of his older brother, Tamerlan.

A second Chechen friend since boyhood, 18-year-old Baudy Mazaev, said that the older brother and their mother, Zubeidat Tsarnaeva, “had a deep religious epiphany” about two or three years ago. At the time, Tamerlan’s new devotion only irritated Dzhokhar, he said.

He gained American citizenship on Sept. 11, 2012, “and he was pretty excited about it,” said his first-year dorm mate, Mr. Rowe. Yet the previous March, he had written “a decade in america already, I want out,” followed in April by “how I miss my homeland #dagestan #chechnya.” And days before his citizenship ceremony, he expressed wonder at why more people did not realize that the 2001 attack on the World Trade Center “was an inside job.”