Dzhokhar Tsarnaev was born in July 1993 in the former Soviet republic of Kyrgyzstan, the youngest of four children in a family that roamed for decades across the Caucasus and Central Asia looking for a stable home.

He spoke only broken English in 2002 when his father, Anzor, an ethnic Chechen, brought him to Massachusetts from the mostly Muslim region of Dagestan in Russia, eventually winning asylum by claiming political persecution. But by the time he entered Cambridge Rindge and Latin School in 2007, he spoke with barely a trace of an accent, blending seamlessly into a student body that was a mélange of immigrants and American-born students of all colors.

By all accounts, he thrived there. Jahar, as his fellow students called him — the rough pronunciation of his Caucasian name, adopted as his nickname — became a star student, winning a $2,500 scholarship upon his graduation in 2011. He loved literature and world history, particularly studies of his former homelands.

In sophomore year, he joined the school’s wrestling team as a novice and quickly grew so strong and skillful, one teammate said, that he could take down even coaches. His teammates say they looked up to him as a teacher and motivator. “We’d be running stairs for hours,” said another, Zeaed Abu-Rubieh, now 21. “Every time I’d stop, when I was thinking about leaving, he’d push me forward, physically push me. And he was strong. He’d say: ‘Go on. Run. You can do it.’ He believed in people.”

His teammates eventually voted him captain. One of the coaches, Peter Payack, said he deserved it. Despite the draining four-hour daily practice and trips at sunrise to weekend meets, he said, Mr. Tsarnaev maintained his academic record and proved a model of good sportsmanship and steady temperament.

“You always see people’s personality traits over the course of a season,” he said. “If somebody is short-tempered, if they lose a match, maybe they throw a chair. There’s somebody who’s moody, or like a loner. He was none of those things.