Janet Napolitano says that the Department of Homeland Security did know that Tamerlan Tsarnaev went to Russia last year, despite the misspelling on his travel documents.
That still leaves the question of why they didn’t do more to check him out and keep an eye on him.
I think in general our government sees the issue of radicalized Chechens as Russia’s problem, not ours. The Chechens have been fighting Russian domination for three hundred years. But we need to recognize that while some of these folks just want to attack Russia, and so their struggle is primarily local and political*, others are more committed to global Islamic jihad, and that is everybody’s problem.
* Of course there are religious factors inextricably interwoven with the fight for Chechen political independence. Under the czars and the post-Soviet regime, they were and are Muslims fighting Christians. Under the Communists, they were Muslims fighting official atheism.