The two Chechen brothers - one a naturalised resident and other a lawful resident - allegedly constructed sophisticated weapons inside the US, a top American Senator has said.
"They constructed the weapons inside the United States. Did they have some sort of training or inspiration or coaching inside or outside the United States? That's all still under investigation.
"We don't have the answer to it yet, but it's pretty obvious these were somewhat sophisticated weapons," Republican Senator Saxby Chambliss told reporters at the Capitol Hill .
On Tuesday, members of the Senate Intelligence committee were given a briefing on the Boston bombings by the Federal Bureau of Investigation and other federal authorities.
The FBI briefing was closed doors, but some members of the Senate Intelligence Committee spoke to the press after the briefing.
"This is an ongoing investigation. It's very fluid. We've gotten minimal information from the individual that's in custody now. But we're going to continue to look at whether or not all information was adequately shared and given to all of the law enforcement agencies. If it wasn't, we got to fix that," Chambliss said in response to a question.
While the younger brother Dzhokhar Tsarnaev, 19, who was arrested by the police last Friday is being treated in a hospital and was charged on Monday, his elder brother Tamerlan, 26, died in an exchange of fire with the police on Thursday.
If convicted Dzhokhar faces death penalty. He is now communicating with the federal investigating authorities in writing.
Senators being encountered by press reporters refrained to give much information arguing that this was a classified briefing.
However, Republican Senator Susan Collins expressed concern over lack of information sharing among various federal agencies.
According to multiple media reports, Dzhokhar has told investigators that he and his brother were motivated by the US war in Afghanistan and Iraq.