Dzhokhar Tsarnaev and Tamerlan Tsarnaev now mysterious to those who knew them

Like any nervous 19-year-old, he was biting his nails.

Dzhokhar Tsarnaev dropped into Gilberto Junior's body shop at about 1 p.m. on April 16, the day after the bombing at the Boston Marathon, to pick up a white Mercedes E350 wagon. He said it was owned by his girlfriend.

Dzhokhar had left the car at the shop two weeks earlier for a new rear bumper. Junior hadn't done the job, yet Dzhokhar took it anyway. Junior had known Dzhokhar and his older brother, Tamerlan, 26, for a couple of years. They would come by the shop with a group of friends and talk to Junior, who is Brazilian, about soccer and Brazilian women.

"He was a normal kid," Junior, 44, said of Dzhokhar. Junior had no hint that the Tsarnaev brothers were suspects in the attack until later in the day. Before long, Tamerlan would be killed in a confrontation with police and Dzhokhar would be the subject of a manhunt that shut down colleges, transit service and sporting events throughout the Boston area.

Dzhokhar was apprehended last night at a house in Watertown, Massachusetts, where he was believed to be hiding after an almost 24-hour search. He was taken to Massachusetts General Hospital for treatment of serious wounds suffered in a gunfight with police the night before, authorities said.

With the aftermath of the bombing still unfolding and information changing by the hour, one constant has been that the brothers didn't appear to be fanatics.

While some dark details of their lives will likely emerge at some point, so far their motivations remain a mystery.

STANDARD TRAPPINGS

Their lifestyle included many of the standard trappings of adolescence and young adulthood, including various social media postings with vague musings about life, love and, in some cases, Islam, though the postings are generally low-key.

Authorities haven't yet found connections to any groups or other suspects, said a person briefed on the investigation who asked for anonymity because the probe continues.

U.S. intelligence agencies reviewing volumes of international communications and other intelligence on terrorism had found no evidence, so far, that the Boston bombers were members of or inspired by any foreign terrorist organization, said a U.S. official who spoke on the condition of anonymity because intelligence matters are classified. Nor were they encouraged by contacts with Islamic or other extremists overseas, the official said.

STRADDLING CULTURES

The brothers, who lived in Cambridge, came from the former Soviet Union to Massachusetts about a decade ago. They left evidence, including on the Internet, that shows them straddling two cultures, an America focused on entertainment and consumerism and a Muslim faith tradition that emphasized devotion and purity.

A profile attributed to Dzhokhar on the Russian social networking site VK lists "career and money" as his personal priority and Islam as his world view.

Tamerlan was a competitive boxer, an aspiring engineer and a devout Muslim.

Tamerlan was born in Russia and his younger brother in the central Asian nation of Kyrgyzstan, said two U.S. law- enforcement officials familiar with the investigation. The brothers and two sisters came as refugees to the Dagestan city of Makhachkala in October 2001 from Kyrgyzstan, said Emirmagomed Davudov, the director of Gimnasium Number 1, where Tamerlan went to seventh grade and Dzhokhar to first grade.

GAINING ASYLUM

The parents first received asylum in the U.S. and then filed for the children, who were given "derivative asylum status" and didn't come through the refugee-admissions program -- though the legal standard is essentially the same, said a State Department official who requested anonymity to discuss the case.

Tamerlan was the extrovert and Dzhokhar the introvert, John Curran of Watertown, Tamerlan's former boxing coach who hadn't seen them in a few years, told NBC News.

"The young brother was like a puppy dog following his older brother," Curran said.

The Russian newspaper Izvestia published what it said was an interview yesterday with the suspects' father, Anzor Tsarnaev, who lives in the Russian region of Dagestan. In it, he said his oldest son was happily married to an American and had a child.

The father said he talked with Tamerlan right after the terror attack, to ask if he was all right, and Tamerlan said, "We are fine, don't worry, we didn't go there." 'Set Up' Their mother, Zubeidat Tsarnaeva, told Russian TV network RT: "I am 100 percent sure that they were set up. Both of my sons are innocent. My youngest son has been in America since he was 8. We never talked about terrorism at home. My eldest son became interested in religion five years ago. He began to follow rules of Islam, but he never said he plans to enter the road to jihad."

Tamerlan was registered as an amateur boxer in 2003-2004 and 2008-2010. He competed in the U.S. National Golden Gloves competition in Salt Lake City in 2009 in the heavyweight division and was the subject of a 2010 photo essay entitled "Will Box for Passport: An Olympic Drive to Become a United States Citizen" in Boston University's student magazine.

In the magazine, he said, he hoped to become an engineer, loved the movie "Borat," and didn't smoke or drink alcohol, given his faith. While he'd lived in the U.S. for years by then, he said, "I don't have a single American friend. I don't understand them." Fleeing Chechnya He told the magazine his family fled Chechnya in the early 1990s to escape the conflict there between Chechen separatists and the Russian military.

Tamerlan was arrested in 2009 on an assault and battery charge and wasn't convicted, according to Stephanie Guyotte, a spokeswoman for the Middlesex County, Massachusetts, district attorney. Additional details weren't available Friday because the courthouse was closed, she said.

Tamerlan spent about seven months in Russia last year, flying out of New York, according to two law enforcement officials who asked not to be identified.

Both brothers had a social network presence, though Dzhokhar's was more robust.

While it is difficult to know for sure whether a Twitter, Facebook or another social-network account is genuine, all indications are that the most insightful account he had was on a Russian site called VK. His page showed that he logged on since the Boston attack, most recently on the morning of April 19, and featured four posts, including a whimsical video making fun of accents of people from the Caucusus region.

POLICE DRIVING

It also contained a joke: "A question is asked at a school: A car is rolling. Inside are a Dagestani, a Chechen and an Ingush. Question -- who is driving the car? Answer: The police." The page also linked to a video that showed bloodied and wounded people in Syria being stepped on or hunted by soldiers.

Tamerlan appeared to have a Google+ account, with 17 people having him in their circles. He also subscribed to a channel on YouTube called "Allah is the One," and commented on a video, which recounts a Russian's conversion to Islam.

In a post two months ago, Tamerlan said, "You accepted Islam not because you believe in it, but because of your own passions and interests (and which Allah knows) that you followed. You entered Islam, and as quickly exited it. You betrayed yourself." A month ago, Tamerlan reposted the same comment on a different Russian site, Mirtesen.ru, which has several videos recounting personal experiences of conversion to Islam.

CRITICIZING LEADER

While some of the online videos have militant or jihadist themes, they don't appear to promote violence against the U.S. The only explicitly political video takes aim at the Russian-supported leader of the republic of Chechnya, Ramzan Kadyrov.

However, several videos have been deleted from the site, including two originally posted under the heading "terrorists."

In a black-and-white photo posted in 2012 on his Russian social network page, Dzhokhar, the younger brother, wears a mop of hair, a dark shirt and a serious expression. He links to several Chechen-related groups, while a video posted April 9 on his page purportedly shows images of atrocities in Syria and ends with the Russian phrase, "Syria calls. We answer." Dzhokhar attended Cambridge Rindge and Latin School, a prestigious public high school in Cambridge that's known for its eclectic, diverse student body.

Among others it educated were actor-director Ben Affleck and basketball player Patrick Ewing.

Getting Scholarship In 2011, Dzhokhar received a higher-education scholarship from the city of Cambridge. On Sept. 11 of the following year, he became a U.S. citizen, law enforcement officials said. The University of Massachusetts Dartmouth said he was registered as a student there. He worked intermittently during his high school years as a lifeguard at Harvard University, the school said, most recently last summer.

Agustin Nedina, an 18-year-old from Cambridge who attended middle and high school with Dzhokhar, said he once played computer games at the suspect's home.

"The one thing I remember clearly is he was playing lots of violent shooting games," said Nedina, who graduated from high school in 2012, a year behind Dzhokhar. Nedina said the games Dzhokhar favored weren't in English.

"He was a quiet kid," he said.

MAKING FRIENDS

Nedina said Dzhokhar was on the wrestling team.

"He wasn't one of the popular kids, but he had a good number of friends," Nedina said.

Both brothers attended Cambridge Community Charter School, a public, tuition-free, college-preparatory charter school in the Kendall Square area near the Massachusetts Institute of Technology. Tamerlan attended Bunker Hill Community College as a part-time student in the accounting program for three semesters between 2006 and 2008.

Ty Darros, 21, said he hung out with Dzhokhar a dozen or so times and last saw him about eight months ago. He said he was surprised to learn that Dzhokhar is suspected in the bombings.

"He was such a nice guy," he said. "The strangest thing about it is that I can't think of anything about him that was strange." Sherry Hamby, a research professor at Sewanee, the University of the South, who is also editor of Psychology of Violence, a scientific journal, said events like the bombing of the marathon seem incomprehensible but often offer common themes that might be seen in the case of the Tsarnaevs.

'MORAL DISENGAGEMENT'

Most perpetrators of violence are in a state of "moral disengagement," said Hamby, who hasn't met or spoken with the suspects. These offenders believe that they've been seriously provoked and that their actions, which almost anyone else would see as heinous, are reasonable under the circumstances.

"The stereotype is that these people are completely psychotic and divorced from reality," she said. "In fact, in other domains of their lives, they aren't divorced from reality at all. They nearly always tend to think of themselves as good guys."

Some immigrants who perceive themselves to be on the fringes of society can begin to harbor these types of feelings, said Usha Tummala-Narra, an assistant professor, counseling psychology at Boston College in Chestnut Hill. When some people have trouble blending into society, they may find their way to others who have similar feelings of alienation, she said.

'NEVER BELONGED'

"Sometimes a person can look like they're blending into mainstream culture, and dress like they have, and go to parties and the rest of it, but they may feel like they never belonged," said Tummala-Narra, who also never met or spoke with either of the brothers. "That might be a critical part of the story." Brothers like the Tsarnaevs might have formed a kind of "cocoon" mentality, similar to Eric Harris and Dylan Klebold, the two high school seniors who killed 13 people and injured 24 in the 1999 Columbine High School massacre in Colorado, Tummala- Narra said.

"It's a way of creating your own safety in a world that doesn't seem quite safe," she said.

While the younger brother has been described as good student and warm-hearted, his behavior may have been influenced by his older brother, said James Alan Fox, a professor of criminology, law and public policy at Northeastern University, one of the Boston colleges that remained closed on Friday.

"It's not just an anti-American or Islamic jihadist ideology, it's the relationship between the two perpetrators," said Fox, who was interviewed by telephone while he was locked inside his Boston home. "They brought out the very worst in each other.

Individually, they may have seen like nice guys. But together they create a different entity."