What did Russia know, and when did it know it, about the two brothers who launched a terrorist attack on the Boston Marathon a year ago? As the anniversary date approaches, a new report from the Inspector General of the Intelligence Community largely lets the FBI off the hook for not identifying Tamerlan Tsarnaev as a domestic threat. Instead, the IG finds that Russia withheld critical information from the US about Tsarnaev’s activities, including a phone call recording in which the older brother discussed Islamic jihad … with his mother, as the New York Times reports:

Russian officials had told the F.B.I. in 2011 that the suspect, Tamerlan Tsarnaev, “was a follower of radical Islam and a strong believer” and that Mr. Tsarnaev “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.”

But after an initial investigation by the F.B.I., the Russians declined several requests for additional information about Mr. Tsarnaev, according to the report, a review of how intelligence and law enforcement agencies could have thwarted the bombing.

At the time, American law enforcement officials believed that Mr. Tsarnaev posed a far greater threat to Russia.

The new inspector general’s report found that it was only after the bombing occurred last April that the Russians shared with the F.B.I. the additional intelligence, including information from a telephone conversation the Russian authorities had intercepted between Mr. Tsarnaev and his mother in which they discussed Islamic jihad.

The IG concludes that the FBI did a proper investigation with the information they received, but they could have worked a little harder to expand their knowledge of the Tsarnaevs, too:

While the review largely exonerates the F.B.I., it does say that agents in the Boston area who investigated the Russian intelligence in 2011 could have conducted a few more interviews when they first examined the information.

Despite the elder Tsarnaev’s travels to Dagestan and his apparent connections to unrest in the region, neither the FBI nor the IG could find any evidence that Tsarnaev or his brother Dzokhar belonged to a terrorist organization. They acted on their own volition, it seems. Without the two Tsarnaevs connecting to a wider network for support in this attack, it’s doubtful that the FBI could have stopped it all by themselves, either.

That doesn’t mean that the FBI should be let off the hook entirely, though. One senior official called them “homegrown violent extremists,” but that’s not quite the case either. The months-long trip that Tamerlan took to Dagestan had to have played a significant role in his radicalization. If anything, the lesson from that information is that foreign-born American residents who stay for months in areas known for radical Islamist violence should come under more scrutiny than Tsarnaev did, regardless of how much information the governments of those regions share.

Lindsey Graham called this failure “a mistake” after the trip to Dagestan became public knowledge, saying, “It’s people like this that you don’t want to let out of your sight.” Hopefully we’ve learned that lesson now.

CNN also reported on the IG’s conclusions this morning: