In 2011, the FBI reportedly interviewed Tamerlan Tsarnaev, the Boston bombing suspect who died in a shoot-out with police, about possible ties to Chechen terrorists. According to reports, though, law enforcement did not pursue him beyond the initial interview.
From Reuters, which cites an unnamed source in law enforcement:
The source said the FBI's dealings two years ago with Tamerlan Tsarnaev occurred following a request from an unidentified foreign government.
The FBI did not produce any "derogatory" information on Tsarnaev and agents then put the matter "to bed," said the source, who spoke on condition of anonymity.
The Washington Post had a similar report on Friday, identifying the "foreign government" in question as Russia:
The FBI confirmed Friday that its agents in Boston had interviewed Tamerlan Tsarnaev in 2011 at the request of a foreign government. A law enforcement official said the request came from the Russian government, concerned about Tsarnaev’s potential ties to Chechen terrorists. But after that interview, the FBI did not follow him further, officials said.