Dzhokhar Tsarnaev was an all-star wrestler at Cambridge Rindge and Latin High School.

The younger one — the one their father described as “like an angel” — gathered around him a group of friends so loyal that more than one said they would testify for him, if it came to that.

The older one, who friends and family members said exerted a strong influence on his younger sibling — “He could manipulate him,” an uncle said — once told a photographer, “I don’t have a single American friend. I don’t understand them.”

A kaleidoscope of images, adjectives and anecdotes tumbled forth on Friday to describe Tamerlan Tsarnaev, 26, and Dzhokhar Tsarnaev, 19, the two brothers suspected of carrying out the bombings at the Boston Marathon that killed three people and gravely wounded scores more.

The one who was on the loose was taken into custody on Friday evening. He was the younger of the two, Dzhokhar Tsarnaev, 19. The elder, Tamerlan Tsarnaev, 26, was killed in a confrontation with authorities, but not before participating in the fatal shooting of an M.I.T. police officer, the carjacking of an S.U.V. and the shooting of a transit police officer, who was critically injured.

They were from Chechnya. Tamerlan was a boxer; Dzhokhar, a college student.

What no one who knew them could say was why the young men, immigrants of Chechnyan heritage, would set off bombs among innocent people. The Tsarnaevs came with their family to the United States almost a decade ago from Kyrgyzstan, after living briefly in the Dagestan region of Russia. Tamerlan, who was killed early Friday April 19, 2013 morning in a shootout with law enforcement officers, was 15 at the time. Dzhokhar, who was in custody the same evening, was only 8.

In America, they took up lives familiar to every new immigrant, gradually adapting to a new culture, a new language, new schools and new friends.

“A picture has begun to emerge of 26-year-old Tamerlan Tsarnaev as an aggressive, possibly radicalized immigrant who may have ensnared his younger brother Dzhokhar — described almost universally as a smart and sweet kid — into an act of terror.”

Clip_161Dzhokhar, a handsome teenager with a wry yearbook smile, was liked and respected by his classmates at Cambridge Rindge and Latin School, where celebrities like Ben Affleck and Matt Damon had walked the halls before him. A classmate remembered how elated he seemed on the night of the senior prom. Wearing a black tuxedo and a red bow tie, he was with a date among 40 students who met at a private home before the event to have their photos taken, recalled Sierra Schwartz, 20.

“He was happy to be there, and people were happy he was there,” Ms. Schwartz said. “He was accepted and very well liked.”

A talented wrestler, he was listed as a Greater Boston League Winter All-Star. “He was a smart kid,” said Peter Payack, 63, assistant wrestling coach at the school. In 2011, the year he graduated, was awarded a $2,500 scholarship by the City of Cambridge, an honor granted only 35 to 40 students a year.

For Tamerlan, life seemed more difficult.

Clip_204A promising boxer, he fought in the Golden Gloves National Tournament in 2009, and he was noticed by a young photographer, Johannes Hirn, who took him as a subject for an essay assignment in a photojournalism class at Boston University. “There are no values anymore,” Tamerlan said in the essay, which was later published in Boston University’s magazine The Comment. “People can’t control themselves.”

Anzor Tsarnaev, the brothers’ father, who returned to Russia about a year ago, said in a telephone interview there that his older son was hoping to become an American citizen — Dzhokhar became a naturalized citizen in 2012, but Tamerlan still held a green card — but that a 2009 domestic violence complaint was standing in his way.

“Because of his girlfriend, he hit her lightly, he was locked up for half an hour,” Mr. Tsarnaev said. “There was jealousy there.” Tamerlan later married and had a small child. He was interviewed by the FBI in 2011 when a foreign government asked the bureau to determine whether he had extremist ties.

Yet Dzhokhar admired and emulated his older brother.

Peter Tean, 21, a high school wrestling teammate, said that he thought Dzhokhar’s intense interest in rough-and-tumble sports came from a desire to be like his brother.

“He’s done these violent sports because his brother’s a boxer,” Mr. Tean said. “He really loves his brother, looks up to him.”

At the University of Massachusetts Dartmouth, Dzhokhar began to struggle academically.

According to a university transcript, he was failing many of his classes. The transcript shows him receiving seven failing grades over three semesters, including F’s in Principles of Modern Chemistry, Intro to American Politics and Chemistry and the Environment. According to the transcript, Dzhokhar received a B in Critical Writing and a D and D-plus in two other courses.

San, 22, a former classmate at the university who would identify himself only by his first name, said that Dzhokhar had told him he was having trouble in some courses.

“He was talking about how he wasn’t doing as good as he expected,” San said. “He was a really smart kid, but having a little difficulty in college because going from high school to college is totally different.”

San said that he would be willing to testify on Dzhokhar’s behalf. “I feel like all of his friends would do that,” he said.

In Cambridge, where Dzhokhar lived in the third-floor unit of a caramel-colored wood-frame triple-decker on Norfolk Street, the brothers were often seen together. It is a multicultural neighborhood where hardware stores and butcher shops are mixed with cafes and Brazilian and Portuguese restaurants. Neighbors said that people were constantly coming and going at the apartment and that they were uncertain who lived there and who was just visiting. Sometimes they saw people from the unit in the backyard. Tamerlan was fond of doing pull-ups on the trellis, they said.

The brothers’ uncle Ruslan Tsarni, 42, said that on the night before he was killed, Tamerlan had called Mr. Tsarni’s older brother. “He said to my brother the usual rubbish, talking about God again, that whatever wrong he had done on his behalf, he would like to be forgiven,” said Mr. Tsarni, who lives in Montgomery Village, Maryland., outside Washington. “I guess he knew what he had done.”

Both brothers had a substantial presence on social media sites.

On VKontakte, Russia’s most popular social media platform, Dzhokhar described his worldview as “Islam” and, asked to identify “the main thing in life,” answered “career and money.” He listed a series of affinity groups relating to Chechnya, where two wars of independence against Russia were fought after the Soviet Union collapsed, and a verse from the Koran: “Do good, because Allah loves those who do good.”

Their father said that Tamerlan would take his younger brother to Friday Prayer, but dismissed the idea that Dzhokhar had become devout, saying that they sometimes caught him smoking cigarettes.

“Dhzokhar listened to Tamerlan, of course, he also listened to us,” he said. “From childhood it was that way. He had his own head on his shoulders, he was a very gifted person. He had a gift of kindness, calmness, fairness — you understand, goodness? For him to do what they’re saying, it doesn’t it doesn’t fit him at all, it is not possible. Not at all.”

In Kyrgyzstan, the Tsarnaevs were part of a Chechen diaspora that dates back to 1943, when Stalin deported most Chechens from their homeland over concerns they were collaborating with the invading Nazi Army. Most returned to Chechnya in the 1950s, after the death of Stalin and lifting of the deportation order, but some stayed. The deportation was a searing, and in some cases, radicalizing experience.

Adnan Z. Dzarbrailov, the head of a Chechen diaspora group in Kyrgyzstan, said in a telephone interview that the Tsarnaev family lived near a sugar factory in the small town of Tokmok, about 40 miles from Bishkek, the capital of Kyrgyzstan. The last member of the family left years ago, he said. He described them as “intelligentsia” and said that Dzhokhar and Tamerlan’s aunt was a lawyer.

Yet that history does little to explain how the brothers became wanted criminals in a horrific act of terrorism, their images captured on grainy surveillance tape and broadcast across the nation.

Gilberto Junior, who owns an auto body shop in Somerville, just saw them as “regular kids,” even if they had a taste for expensive cars.

So it did not especially alarm him when Dzhokhar rushed in on Tuesday, April 16, the day after the bombing, and said he needed his car immediately, never mind that the repairs had not been done and the white Mercedes wagon had no bumper and no taillights.

The younger Tsarnaev brother seemed nervous, he said. He was biting his nails and his knees were bending back and forth a bit; it occurred to Mr. Junior that he might be on drugs.

“At the time I didn’t think about anything,” Mr. Junior said. “How could I judge him? I knew that he was nervous.”

One Zaur Tsarnaev, identified as a 26-year-old cousin of the suspects, said, “I used to warn Dzhokhar that Tamerlan was up to no good.” Tamerlan “was always getting into trouble,” he added. “He was never happy, never cheering, never smiling. He used to strike his girlfriend. He hurt her a few times. He was not a nice man. I don’t like to speak about him. He caused problems for my family.”

But what about that image of Dzhokhar as sweet?

On Friday, BuzzFeed and CNN claimed to verify Dzhokhar’s Twitter account. The tweets posted on that account give a window into a bifurcated mind — on one level, a middle-of-the-road 19-year-old boy, but on another, a person with a mind leaning toward darkness.

Like many young people, the person tweeting from that account liked rap music, saying of himself, “#imamacbookrapper when I’m bored,” and quoting rap lyrics in his tweets.

He tweeted quite a bit about women, dating and relationships; many of his musings were misogynistic and profane. Still, he seemed to want to have it both ways, to be rude and respectful at once, tweeting on Dec. 24, 2012: “My last tweets felt too wrong. I don’t like to objectify women or judge anyone for their actions.”

He was a proud Muslim who tweeted about going to mosque and enjoying talking — and even arguing — about religion with others. But he seemed to believe that different faiths were in competition with one another. On Nov. 29, he tweeted: “I kind of like religious debates, just hearing what other people believe is interesting and then crushing their beliefs with facts is fun.”

His politics seemed jumbled. He was apparently a 9/11 Truther, posting a tweet on Sept. 1 that read in part, “Idk why it’s hard for many of you to accept that 9/11 was an inside job.” On Election Day he retweeted a tweet from Barack Obama that read: “This happened because of you. Thank you.” But on March 20 he tweeted, “Evil triumphs when good men do nothing.” This sounds like a take on a quote from Edmund Burke, who is viewed by many as the founder of modern Conservatism: “The only thing necessary for the triumph of evil is for good men to do nothing.”

Dzhokhar Tsarnaev had strong views on the Middle East, tweeting on Nov. 28, “Free Palestine.” Later that day he tweeted, “I was going to make a joke about Hamas but it Israeli inappropriate.”

Toward the end of 2012, the presence of dark tweets seemed to grow — tweets that in retrospect might have raised some concerns.

He tweeted about crime. On Dec. 28 he tweeted about what sounds like a hit-and-run: “Just saved a bunch of money on my car insurance by switching my car into reverse and driving away from the accident.” And on Feb. 6 he tweeted, “Everything in life can be free if you run fast enough.”

He posted other tweets that could be taken as particularly ominous.

Oct. 22: “i won’t run i’ll just gun you all out #thugliving.”

Jan. 5: “I don’t like when people ask unnecessary questions like how are you? Why so sad? Why do you need cyanide pills?”

Jan. 16: “Breaking Bad taught me how to dispose of a corpse.”

Feb. 2: “Do I look like that much of a softy?” The tweet continued with “little do these dogs know they’re barking at a lion.”

Feb. 13: “I killed Abe Lincoln during my two hour nap #intensedream.”

The last tweet on the account reads: “I’m a stress free kind of guy.” The whole of the Twitter feed would argue against that assessment.