Tamerlan Tsarnaev was 26 years old, a champion boxer, an Olympic hopeful, and a married father of a 3-year-old girl, who spent six months in Russia last year.
19-year-old Dzhokhar Tsarnaev was a high school wrestler, a pre-med college student, and like his older brother a naturalized U.S. Citizen.
Eyewitness News is learning more about these two brothers, but not nearly enough to explain what triggered their violence.
It increasingly appears that the older one had some kind of hold over his younger, more impressionable sibling.
"What suddenly triggered this?" said Richard Barrett, a counterterrorism specialist.
The former analyst for Britain's Intelligence Agency says something had to be going badly, probably with the older brother, to turn them into terrorists.
"There has to be something really quite personal that really involves the individual, they get really worked up about something," Barrett said.
The older brother seemed to struggle more in America.
At one point, he was charged with beating his former girlfriend and even returned for a time last year to Russia.
But what would cause him and his brother to go to this extreme.
Their uncle made one suggestion.
"What's behind this it's being losers, not being able to settle themselves and thereby hated everyone," said Russian Tsarni, the suspects' uncle.
Family and friends say there seemed to be no outward signs of the hatred the two brothers had for Americans:
"Incredibly hard to predict who might do something like this," Barrett said.
The older brother was married and had a 3-year-old child.
Just weeks after he returned from a trip to Russia and Chechnya last summer, he became a U.S. citizen on September 11, 2012.
A cousin says he believes the older brother ensnared his younger sibling, whom he described as sweet and smart.
The cousin says he kept warning Dzhokhar that his brother was up to no good.
Dzhokhar became a U.S. citizen last year on September 11th.
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