There are growing concerns from Washington to treat Dzhokhar Tsarnaev - an American citizen, as an enemy combatant, not a criminal defendant. That would mean denying him certain constitutional protections.
But how could two young men who call this country home become suspected terrorists?
The brothers Tsarnaev had been in the United States for nearly a decade. Ethnic Chechens, they came with their family to Cambridge -- fleeing violence in their homeland for a better life in America. Immediately, 8-year-old Dzhokhar immediately seemed to just fit in.
Larry Aaronson, a history teacher at the prestigious Cambridge Rindge and Latin High School -- the same school Matt Damon and Ben Affleck attended - said Dzhokhar was a great kid.
"I know this kid to be compassionate. I know this kid to be forthgoing. He's a great athlete, a sportsman, he's never been in trouble,"
Aaronson said. "He was just generous, he was compassionate, he was thoughtful."
A steller athlete, Dzhokhar was the captain of his high school wrestling team and he was popular.
"Lots of friends on the teams. I mean, he was always with other kids.
He's not a loner. He was not a loner. He's not anybody like that," said Aaronson.
Dzhokhar was so impressive, that in 2011 -- the year of his high school graduation -- he won a $2,500 dollar educational scholarship from the City of Cambridge. He enrolled at the University of Massachusetts Dartmouth and chose to study nursing, talking about wanting to help people.
"I never saw him out of emotion, never in rage, he was just a real relaxed kid," friend Francis Barry, a sophomore said he liked hanging out with him.
"It still hasn't sunk in that the kid on my couch was the kid planting bombs in Boston," he said.
"There's nothing about him that would suggest anything like this - politics, religion -- nothing," said Aaronson.
On Sept. 11, 2012, Dzhokhar took the oath to become an American citizen.
On the surface, at least, the younger Tsarnaev brother seemed to be thriving in America, but his older brother, Tamerlan, was clearly struggling. The 26-year-old once had dreams of boxing in the Olympics, representing the United States.
Julian Pollard was one of his sparring partners. Tamerlan was a top Golden Gloves boxer. But for all his talent, it seems he still didn't feel entirely welcome here, telling a photographer who took photos published in 2010, "I don't have a single American friend because I don't understand them."
"The first year I met him, he had on like, leather pants and snakeskin boots," Pollard recalled. And then Pollard noticed a big change in Tamerlan.
"The second year when I saw him, he had on a T-shirt, hoodie and jeans," he said. "... the way he carried himself was much more humble. He was, ah, he only spoke about his faith. He was big into religion."
Tamerlan attended a Mosque in Cambridge with his brother. On Saturday, a spokeswoman said it is cooperating with authorities and issued a statement:
"In their visits they never exhibited any violent behavior, sentiments, otherwise they would have been immediately reported to the FBI," she said.
CBS News spoke by phone to a woman whose friend became Tamerlan's wife and the mother of his child.
"He just seemed like a really normal average guy when we met him and then really started to change," the woman said. "He became very violent toward her and was brainwashing her into converting into Muslim."
In 2009 a domestic violence complaint reportedly was filed against Tamerlan. In Russia on Friday, Tamerlan's father told a reporter the complaint was the reason his eldest son never became an American citizen.
His wife's family commented on the marathon bombings saying they were "sickened by the horror he has inflicted."
At least five years before the bombing, Tamerlan's life started to take a dark turn. He dropped out of community college and his close friend was murdered.
The victim's throat was slit and marijuana was sprinkled over the body. A search of social media sites shows two very different sides to Tamerlan: on one he jokes around about regional accents.
And on another site, he posted videos on YouTube that feature Muslim extremism.
But there's no evidence yet tying Tamerlan or his brother to any Islamic extremists. In Russia on Friday, their father defended them.
"My boys never even saw weapons," he said, "except maybe on TV."
But this was a Chechen family with roots in a region that had seen bloody civil war and serious incidents of terrorism.
In 2002, Chechen militants took more than 800 theater goers hostage in Moscow; 130 hostages died.
And two years later in Beslan, militants took more than 1,000 people hostage and killing more than 300 - most of them children.
Just a few years before the Boston bombings, big changes happened in the brothers Tsarnaev's lives. Their father left the United States, moving to Russia and leaving Tamerlan to take on a more paternal role in his younger brother's life. Dzhokhar's friends noticed.
"His older brother didn't approve of his partying lifestyle. Religious and he really didn't condone drinking and partying and that stuff," said Barry.
The question now is did the older brother's influence go further than that?