U.S. officials say the oldest of the two brothers suspected in the Boston Marathon bombings was placed on a counterterrorism list in late 2011.
The officials say the CIA asked that Tamerlan Tsarnaev's name be placed on the list after it was contacted by the Russian government with its concerns that he had become a radical Islamist.
Moscow also issued a similar warning to the FBI on Tamerlan Tsarnaev earlier in 2011. Officials say the agency launched an investigation, but eventually concluded he posed no threat.
U.S. lawmakers have raised concerns about information sharing between law enforcement and intelligence agencies in the aftermath of the April 15 twin bombings that left three people dead and 264 others injured - including at least 14 who lost limbs. Authorities will brief the full U.S. Senate on the investigation into the bombing.
Investigators say Tamerlan, 26, and his brother Dzhokar, 19, placed the bombs near the finish line of the Boston Marathon. Tamerlan was killed in a shootout with police last Thursday, while Dzhokhar was captured a day later.
Dzhokhar has been charged with using a weapon of mass destruction. He is in federal custody in a Boston hospital.
Several months after he first came to the attention of U.S. federal agents, Tamerlan Tsarnaev left the U.S. in January 2012 for a six-month visit to Russia. When he returned, his name generated an alert by a screening system used by U.S. Customs agents. But Republican Senator Lindsey Graham said the FBI told him it was not aware at the time of Tsarnaev's trip to Russia.
U.S. investigators have questioned the suspects' parents in the Russian republic of Dagestan to determine if Tamerlan had contacts with Islamic extremists during his 2012 visit. The family is originally from Chechnya, where Muslim insurgents have been engaged in a bloody conflict with Russia for decades.
U.S. Vice President Joe Biden denounced the suspects Wednesday in Boston. Biden spoke at a memorial service for a university police officer allegedly gunned down by the suspects just days after the bombings.
"Why, whether it’s al-Qaida central ... or two twisted, perverted, cowardly, knock-off jihadists here in Boston. Why do they do what they do?” he asked.
Several thousand mourners gathered at the Massachusetts Institute of Technology to remember the slain policeman, Sean Collier. Biden said the United States must keep its values in the face of threats from terrorists.
Boston authorities on Wednesday reopened Boylston Street to the public. It is the city thoroughfare where the explosions occurred.