U.S. officials told CNN analyst Tom Fuentes on Sunday they have found no further connection between Tsarnaev and Abu Dujana, but the investigation into his activities overseas continues.
In 2011, before his visit to Russia, Moscow asked the FBI to investigate Tamerlan Tsarnaev in the United States, according to the FBI.
"The request stated that it was based on information that he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel to the country's region to join unspecified underground groups," the FBI said in a statement.
Some details have also emerged about what Tsarnaev did after he returned from Russia, including a January incident at a mosque in Cambridge, Massachusetts.
During a sermon about gaining inspiration from the story of slain civil rights leader Martin Luther King Jr., Tsarnaev interrupted the preacher, the Islamic Society of Boston said in a statement Monday.
Tsarnaev stood up, shouted at the preacher, accused him of "contaminating people's mind" and called him a hypocrite, the society said, citing accounts from congregants.
Some members of the congregation shouted back at Tsarnaev, telling him to "leave now."
Leaders of the mosque later told him he would no longer be welcome at the mosque if he continued to interrupt sermons. At future prayers, he was quiet.