The FBI declined to comment on this story beyond a terse statement it released Friday.
"In early 2011, a foreign government asked the FBI for information about Tamerlan Tsarnaev," the statement said. "The request stated that it was based on information that he was a follower of radical Islam and a strong believer, and that he 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."
FBI officials subsequently acknowledged the "foreign government" referred to in that statement was Russia and that Moscow was concerned about ties Tsarnaev and the other bombing suspect, his younger brother, Dzokhar, had to extremist groups in Chechyna. After receiving this request from Russia, FBI agents in Boston interviewed Tsarnaev, whose family left Chechnya to escape the decades of conflict between the Russian government and rebels there when he was a small child.
Experts who talked to TPM described the request to look into Tsarnaev that the FBI received from the Russian government as a fairly common occurrence.
Dr. Christopher Swift, is a professor at Georgetown University, lawyer, and former Treasury Department official who researches terrorist organizations. His work has taken him to both the Middle East and Chechnya. He said the Russian government often participates in information exchanges with U.S. law enforcement officials about terrorism.
"These are routine," Swift said of Russia's request to the FBI. "On terrorism issues, this is one of the few places where the United States and Russia maintain some semblance of a functional relationship."
Steve Sestanovich, who served as America's ambassador-at-large to Russia from 1997 to 2001 and is currently a senior fellow for Russian and Eurasian studies at the Council on Foreign Relations, agreed it would be fairly standard practice for Russia to reach out to American law enforcement agencies for information about someone applying for a visa to Chechnya, which Tsarnaev reportedly visited during his trip to Russia last year.
"It wouldn't be too surprising for the Russians to ask for information on any Chechen visa applicant -- certainly 20-something males," said Sestanovich.
Both Swift and Sestanovich said that the U.S. government would have had reasons to take Russia's concerns about Tsarnaev with a grain of salt. Swift suggested Russia's desire to stamp out extremists in Chechnya motivates some of the information they distribute about the region and that it is his "understanding" that "the Russians have sent us a lot of bad data in the past."
"One of the things we have to be very careful about is trusting what the Russians tell us, because they have other equities involved. They want to show Chechnya's part of Al Qaeda, when it's not. They want to show things that help them politically that may not necessarily be true," explained Swift. "So, we've got to be very careful about how we do our due diligence on the intelligence the Russians give us."
Sestanovich raised the possibilty the Russians may not actually have had information about Tsarnaev being tied to Chechen rebels.
"Question: Did the Russians really have any information on him, or were they just fishing?" Sestanovich asked.
The specific groups that were the subject of Russia's inquiry about Tsarnaev have not been identified. The Russian embassy in Washington has not responded to a request for comment on this story.
If Russia did indeed have legitimate concerns that Tsarnaev had contact with Chechen extremists, Swift said he's quite sure which organization they would have been referring to: a small group of fierce Islamic fighters called the Caucasus Emirate.
"It would have been the Caucasus Emirate. There's no other group there," said Swift. "The Caucasus Emirate is the only organization down there and the only one that matters."
In recent years, Chechen rebels have moved from a nationalistic ideology to a religious one. According to Swift, a major factor in this shift is the fact the different Chechen rebel groups have, over time, consolidated under the umbrella of Caucasus Emirate, which he describes as "the successor to all the various groups that have been fighting against Russia since the 1990s."
"It's run by a guy named Dokka Umarov. He's a nasty piece of work. Ideologically, he and his movement are very much in the same Salafi jihadi realm as Al Qaeda and movements like Al Qaeda," Swift explained.
Sestanovich, while reiterating that the Russian government's request does not necessarily "mean they had any information linking him to Caucasus Emirate," said the group is often the focus of "official communications between law enforcement and intelligence folks" in Washington and Moscow because it is on the U.S. terrorism watch list. However, he also said a request to look into Tsarnaev for ties to radical Islam "would not be restricted to one group."
Swift also noted that Caucasus Emirate's involvement with an attack on American soil would represent a major departure from its past activities. Despite rhetoric and online propaganda calling for a worldwide Islamic caliphate, Swift said Caucasus Emirate has, thus far, been solely focused on the Caucasus and "within Russia."
"What distinguishes them and what has always distinguished them is their organizational and operational structure is local not global. The message might be global, the propaganda might be global, their ideology might be global ... but their operations and organization has always been local, local, local," said Swift. "They've never done anything overseas."
There is no confirmed information about whether Tsarnaev and his brother acted alone when they allegedly attacked the marathon. Tsarnaev, who was a religious Muslim, seems to have consumed jihadist propaganda online. It's possible he was radicalized on his own and not through any in-person interaction with an established terrorist organization. As both Swift and Sestanovich said, it's also possible he worked with another group, inside or outside of Russia. However, if Tsarnaev did indeed connect with Caucasus Emirate during his trip to Russia last year, Swift said it would explain how he acquired the skills necessary to terrorize a major American city.
"These guys have been fighting constantly for 15 years. They are the epitome of the human fighting machine in terms of their technical proficiency, in terms of their unit cohesion," Swift said of Caucasus Emirate. "They fight very hard, so if someone was there and did get some training, they would have gotten first-rate training."