Tsarnaev, 26, was one of two bothers suspected of setting off two bombs at the Boston Marathon April 15, killing three and wounding more than 260. Tamerlan Tsarnaev was killed by police; his younger brother Dzhokhar Tsarnaev, 19, is in custody.
Mueller said after a tip from Russian officials an FBI investigation of Tamerlan Tsarnaev began in March 2011 and found he posed no threat, The Washington Post reported. Mueller told the panel two more requests for more information from the Russians brought no response.
"As a result of this, I would say, thorough investigation, based on the leads we got from the Russians, we found no ties to terrorism," Mueller told the Senate Appropriations Committee's subcommittee on commerce, justice and science.
The Post said Mueller offered little new on the investigation.
But he conceded electronic notifications that the elder Tsarnaev had left the United States in January 2012 and spent six months in Russia weren't shared with the Joint Terrorism Task Force in Boston.
Interviewed by the FBI before he was charged, Dzhokhar Tsarnaev told FBI agents that he and his brother were motivated by anger at the U.S. wars in Afghanistan and Iraq.