Zubeidat Tsarnaev said the FBI had visited her family "several times" in 2011 with questions about Tamerlan's "Islamic interests."
A senior U.S. official with direct knowledge of information from the Russians said that the case then "was extremely thin," adding that Russia wanted Tamerlan Tsarnaev questioned to see if he and others had become "radicalized." U.S. authorities closed the case a few months after opening it.
Putin: 'We were right'
Russian President Vladimir Putin on Thursday urged closer cooperation between other countries' security services in the wake of the Boston attack
"If we combine our efforts, we will not suffer blows like that," he said during a live televised call-in session in Moscow on Thursday.
The Tsarnaevs are originally from the embattled Russian republic of Chechnya but fled from the brutal wars there in the 1990s. The two brothers were born in Kyrgyzstan and moved at different times to the United States.
In his first on-camera comments since the bombing, Putin also lashed out against those in the West who have slammed Russia for human rights abuses in its actions toward Chechnya.
"Russia is among the first victims, and I hate it when our Western partners call our terrorists -- who committed some heinous crimes in Russia -- when they call them freedom fighters and never call them terrorists. They supported them," said Putin, accusing unnamed people or groups of providing Russia's foes with political, financial and "media" support.
And U.S. authorities have come under fire at home, with lawmakers asking if the FBI and CIA failed to share information. Sources told CNN that Russia had separately asked the FBI and the CIA to look into Tamerlan Tsarnaev in 2011.
Sen. Lindsey Graham, a South Carolina Republican, said Thursday he believes "ultimate blame" for the attacks goes to the Obama administration.
"The FBI and the CIA are, they have great people but, you know, we're going backwards in national security. Benghazi and Boston to me are examples of us going backward," he said.
But a ranking Democrat on a House intelligence subcommittee said Thursday he does not see an intelligence-sharing failure.
"This information was put in a database, it was shared among different agencies, it was shared with a joint terrorism task force, and that's exactly what should happen," U.S. Rep. Adam Schiff, D-California, told CNN, referring to the TIDE database.
Sources: Suspect was unarmed in boat
More details, meanwhile, continue to emerge about the April 15 bombings as well as authorities' engagement days later with the two suspects.
A law enforcement official told CNN Thursday that at least one of the two bombs -- the second to explode -- was detonated by remote control. Rep. Dutch Ruppersberger, a Maryland Democrat and member of the House Select Committee on Intelligence, said that the brothers used a remote control device similar to those used to guide toy cars.
While video taken near the scene of the explosions shows Dzhokhar Tsarnaev talking on a cell phone, it is not known whether he used it to trigger a device, a law enforcement official said.
Those twin blasts killed three people and injured more than 260 others, 14 of whom had limbs amputated. As of Thursday evening, 34 of those wounded were still being treated at Boston hospitals, including one patient in critical condition.
The manhunt for those responsible ended last Friday, when Dzhokhar Tsarnaev was captured after a tense standoff after he'd hidden in a boat in the yard of a home in the Boston suburb of Watertown, Massachusetts.
The teenager was unarmed when he was wounded in a barrage of gunfire, and there was no firearm found in the boat, said several sources from difference agencies familiar with the investigation.
Authorities previously said in a criminal complaint that there was a standoff involving gunfire before Dzhokhar's capture. Watertown Police Chief Edward Deveau told CNN's Wolf Blitzer on Saturday that it was his understanding that the suspect fired from the boat.
This came after Tsarnaev and his older brother allegedly shot and killed Massachusetts Institute of Technology campus police officer Sean Collier in Cambridge.
The Middlesex County District Attorney's Office hopes to bring charges against Dzhokhar Tsarnaev for his alleged role in incidents last week in Cambridge and Watertown, spokeswoman Stephanie Guyotte said Thursday.