U.S. Had Been Warned of Tamerlan Tsarnaev's Radicalization

Russian officials gave the heads-up

Russian authorities warned the FBI in early 2011 that suspected bomber Tamerlan Tsarnaev may have been a follower of "radical Islam," a revelation that raised new questions in Congress on Saturday about whether the Boston Marathon attacks that killed three and wounded more than 170 could have been prevented.

A senior congressional aide privy to the Boston Marathon terror investigation confirmed Saturday that the FBI received the warning after Tsarnaev's apparently suspicious activities caught the attention of Russian authorities keeping close surveillance on militant Islamist groups in the Caucasus region of the former Soviet Union.

The FBI acknowledged Friday that it had investigated Tsarnaev in 2011, even interviewing him and his family, but "did not find any terrorism activity," either domestic or foreign.

"The FBI had this guy on the radar and somehow he fell off," said the congressional aide, who said oversight committees on Capitol Hill are seeking answers from counterterrorism officials. "We heard for several days leading up to this there was no intelligence. Now we know there could have been intelligence."