Russian authorities contacted the US government with concerns about Tamerlan Tsarnaev not once but multiple" times, including an alert it sent after he was first investigated by FBI agents in Boston, raising new questions about whether the FBI should have paid more attention to the suspected Boston Marathon bomber. The FBI has previously said it interviewed Tsarnaev in early 2011 after it was initially contacted by the Russians. Following a closed briefing of the Senate Intelligence Committee Tuesday, Senator Richard Burr, a North Carolina Republican, said he believed that Russia alerted the United States about Tsarnaev in "multiple contacts," including at least once since October 2011. Warnings raised by Russia have loomed large in the investigation of how Tsarnaev, a Kyrgyzstan national, and his younger brother, Dzhokhar, a naturalized US citizen, allegedly prepared for the bombing. US officials have faced tough questions for not tracking the older brother's travels to the Russian provinces of Dagestan and Chechnya, where he spent more than half of 2012 and may have interacted with militant groups or individuals. Senator Lindsey Graham, Republican of South Carolina, said ... that the FBI told him it was not aware of the older Tsarnaev's travels because his name had been misspelled on an airliner passenger list. US Secretary of Homeland Security Janet Napolitano confirmed the misspelling during a hearing before the Senate Judiciary Committee ... but she said Homeland Security nonetheless was aware of his trip.