CBS isn’t letting the thread drop on Tamerlan Tsarnaev’s six-month odyssey in the Caucasus, and neither are federal investigators, apparently. Russian intelligence says that the elder brother in the Boston Marathon bombing met with a suspected militant on several occasions while staying in Dagestan, and the US is taking a closer look at those contacts even as the younger brother insists the two acted alone:

The Wall Street Journal has more:

U.S. investigators are looking into a Russian intelligence report that alleged Boston bomber Tamerlan Tsarnaev met with a suspected militant during his six-month visit to Russia in 2012, according to American law-enforcement officials.

In the aftermath of the bombings, some American counterterrorism officials received information from law-enforcement officials in Makhachkala, Dagestan, detailing alleged contacts between Mr. Tsarnaev and a suspected militant being tracked by Russian officials, according to a law-enforcement official briefed on the Boston Marathon investigation.

It’s not just Tsarnaev that’s being investigated either, but also the FBI:

The accuracy of that report and whether it was shared before the attack in Boston is a subject of debate. According to one account, Russia’s security service told the Federal Bureau of Investigation about it in November. U.S. law-enforcement officials said they didn’t receive any such information and are trying to determine if it is true.

Mr. Tsarnaev’s intersection with Russia security authorities came after he was interviewed by FBI agents in the U.S. in 2011. How these contacts were handled by both countries likely will be critical in determining whether officials missed possible warning signs, and whether poor communications between the two countries hampered cooperation.

Almost immediately after the FBI’s first contacts with Tsarnaev became known, Russia insisted that they tried to warn the US about him, and that the FBI didn’t respond to them. The FBI now claims the same thing about Russian intelligence:

The FBI interview was conducted at Russia’s request and produced no suspicious links, said a senior U.S. law enforcement official. Repeated follow-up questions to Russian authorities about Mr. Tsarnaev went unanswered, U.S. officials said.

It’s possible that Tsarnaev’s six-month trip to Dagestan didn’t produce any contacts with radicals in the area, and that Tamerlan’s decision to conduct terror attacks was entirely independent.  That would make the Dagestan adventure very coincidental, though, and it’s difficult to believe that his sudden fanaticism and identification with radical Islamists on his return less than a year ago had no roots at all in his geographic juxtaposition with radical Islamists in the Caucasus.  So far, it seems that the Russians consider that theory a little fantastical, too.