'Key Thread' in Boston Bombing: Trip to Russia Investigators focus on Tamerlan Tsarnaev's possible extremist links By Evann Gastaldo, Newser Staff Posted Apr 21, 2013 8:39 AM CDT 98 comments Comments In this Feb. 17, 2010, photo, Tamerlan Tsarnaev, left, accepts the trophy for winning the 2010 New England Golden Gloves Championship from Dr. Joseph Downes, right, in Lowell, Mass. (AP Photo/The Lowell Sun, Julia Malakie) (Newser) – As the Boston Marathon bombing investigation continues, the FBI is really zeroing in on dead suspect Tamerlan Tsarnaev's six-month trip to Russia last year, the New York Times reports. The elder of the Tsarnaev brothers visited two predominantly Muslim republics in the country's north Caucasus region—Chechnya and Dagestan—both of which are home to strong militant separatist movements. Russia had warned the FBI that Tsarnaev was a "follower of radical Islam" back in 2011, but law enforcement officials did not deem him a security risk; now some members of Congress are unhappy at the way the tip was handled in advance of Tsarnaev's overseas trip, considering he may have had connections to extremist groups in the area. It was after that trip that he started posting jihadist videos. As federal investigators rush to review the trip (which Tsarnaev's father says was simply to renew his son's Russian passport) and any extremists Tsarnaev may have connected with in Russia, one former senior FBI official calls it "a key thread for investigators and the intelligence community to pull on." But at the time, the FBI never followed up on Tsarnaev after he returned to the US, because it did not have the legal authority to do so after uncovering nothing of note in its initial investigation. The FBI investigation did, however, prevent Tsarnaev from becoming a US citizen; the Department of Homeland Security opted to hold his petition for further review. Sources tell Fox News that investigators are looking into possible connections between Tsarnaev and the Caucasus Emirate, a separatist and extremist Islamic group whose Chechen leader is known as "Russia's Osama bin Laden." And today on Meet the Press, Rep. Mike Rogers, chair of the House Intelligence Committee, said Tsarnaev may have made the Russia trip under an alias.