Intelligence sources tell CNN it is “rare” for Russians to reach out like that, to ask the FBI to look into someone as they did with Tsarnaev.

The FBI interviewed Tsarnaev in 2011, but says it found no terrorism activity at the time. But it appears the bureau did not follow up after Tsarnaev spent six months in Chechnya in 2012. The question is, why?

“There’s going to be a lot of questions, that’s one of them obviously,” said Rep. Michael Capuano, D-Massachusetts. “I’m sure the FBI is going to want to ask those questions of themselves, as well.”…

What is not known now is how many people the FBI interviewed, over what period of time, and whether there was any future surveillance. Also unknown is whether the Russian FSB gave the U.S. a list with many names on it, or just a few – whether it was a standard request, or something more unique that should have warranted more attention.