They were the two young men at the center of Monday's Boston Marathon bombing that killed three and injured more than 150 others.
Investigators say 26-year-old Tamerlan and 19-year-old Dzhokar Tsarnaev placed the bombs near the finish line of the race.
These facts seem unbelievable to those who knew the younger Tsarnaev brother.
"I've hung out with him multiple times -- probably 10 plus times. He's a really cool kid he played sports -- high school sports. He didn't seem like inverted, he was just a really sociable kid who was really friendly," said friend Ty Barros.
The brothers are believed to be from a region of Russia near Chechnya who moved to the U.S. years ago.
By all accounts, Dzhokar and Tamerlan were normal young men making a life for themselves in the U.S.
Tamerlan studied engineering at Bunker Hill Community College and was a boxer who expressed a desire to fight for the U.S. in the Olympics.
Dzhokhar went to school at University of Massachussetts at Dartmouth and became a U.S. citizen on September 11th, 2012.
Experts say these unassuming young men might represent the new face of the terror threat for the United States.
"I think this is the third stage of terrorism, major groups like Al Queda, 90 percent of their membership has been captured or killed," said intelligence expert John Loftus. "They recruit kids and train them online and just hope they do something."
Chechnya has been the scene of two wars between Russian forces and separatists since 1994, in which tens of thousands were killed in heavy Russian bombing. That spawned an Islamic insurgency that has carried out deadly bombings in Russia and the region, although not in the West.
The older brother had strong political views about the United States, said Albrecht Ammon, 18, a downstairs-apartment neighbor in Cambridge. Ammon quoted Tsarnaev as saying that the U.S. uses the Bible as "an excuse for invading other countries."
Also, the FBI interviewed the older brother at the request of a foreign government in 2011, and nothing derogatory was found, according to a federal law enforcement official who was not authorized to discuss the case publicly and spoke on condition of anonymity.
The official did not identify the foreign country or say why it made the request.
(Material from the Associated Press contributed to this report.)
Didn't find what you were looking for?