04/25/2014 06:54 pm ET Updated Jun 25, 2014

The Boston Marathon Bombing One Year Later: What We Still Don't Know

Just over a year removed from the attack on the Boston Marathon, we still know surprisingly little about the person allegedly responsible for its planning and execution, Tamerlan Tsarnaev. While his younger brother Dzhokhar sits in federal custody awaiting trial for his part in the crime that killed three innocent people and wounded hundreds of others, the picture of the conspiracy that has emerged in the months since April 15, 2013 remains cloudy, with major questions remaining about Tamerlan's motives and intentions. As the recently released report on the attack by the House Committee on Homeland Security reflects, several important questions remain unanswered.

The largest glaring hole in our understanding of the Boston Marathon attack centers on how Tamerlan Tsarnaev became radicalized. It seems relatively clear from evidence of his behavior in Greater Boston during the time leading up to the attack that Tamerlan had indeed embraced a radical Islamic ideology. Upon returning from his trip to Russia, he reportedly engaged in several heated altercations at the local Islamic Society of Boston (ISB) cultural center. Investigators also uncovered a YouTube account created by Tsarnaev on which he posted several radical jihadist videos. More recently, evidence emerged that Tsarnaev attempted to change his name to that of a famous Chechen rebel leader, killed by Russia's security services, three months before the attack .

Prior to his much-scrutinized Russian trip (January - July 2012), there are also clues that Tamerlan Tsarnaev had begun down a road to radicalization. He was questioned by FBI agents in early 2011 after receiving a formal request from Russia's internal security service, the FSB. While this indicates that Tamerlan had somehow sparked the interest of Russian intelligence officials, the FBI investigation found little to corroborate Russian concerns and uncovered no connections to terrorism, and while Tsarnaev was placed in requisite databases and watch lists, little else came of the initial questioning.

Thus, it seems clear that the information that would be most useful in understanding Tamerlan Tsarnaev's transformation into a radical Islamic terrorist willing to target innocent civilians in his adopted homeland, relates to his trip to Russia. Given current relations between the United States and Russia, and the more general difficulties associated with information-sharing and cooperation between intelligence services, the answer may never be known, but the critical question is all too clear. What did Tamerlan Tsarnaev do during his trip to Makhachkala, Dagestan from January to July 2012?

There has been a great deal of conjecture related to this question. Tsarnaev's father insists that his son did little, if anything, during the trip. However, the opportunities for an aspiring radical Islamist in Makhachkala would be quite expansive. As the capital city of Dagestan, Makhachkala has become a central point for Islamic radicals fighting a government (and security force) that is perceived as brutal and corrupt. It is also home to a large Islamic community and several Mosques that are viewed as spreading a radical, jihadist message. It is quite possible that Tamerlan spent significant time listening to the sermons of Islamic radicalism and jihad, which perhaps confirmed ideas that he had already been developing. While he may have also engaged in the study of radical Islamic literature on the Internet, this experience may have solidified his own radical thinking and planted the seeds of violent jihadist action.

While there is no hard evidence of any actual meetings, a second potential opportunity for Tsarnaev in Makhachkala would be to actually meet and build ties to radical Islamic terrorists and insurgents operating in the city and throughout the region. The House Committee Report provides the example of Mahmoud Mansour Nidal, a recruiter for Dagestan Islamic insurgency. Prior to his death in May 2012, Nidal operated in Makhachkala and may have met Tsarnaev. Some sources indicate they did indeed meet, but that Tamerlan, while interested in joining the insurgency, was not trusted and therefore his candidacy was rejected. This remains highly uncertain.

Finally, and least likely, Tamerlan Tsarnaev may have (perhaps without his father and family's knowledge) followed many of his young Muslim peers in Mahkachkala "into the forest," or into the actual ranks of the Dagestan insurgency. In such a scenario, he may have received actual training in bomb making and other relevant activities that would provide more or less irrefutable evidence of his commitment to wage violent jihad and also explain the brutal effectiveness of the two devices detonated at the Marathon finish line.

However, as the House Report is careful to premise -- despite significant investigation -- much of this discussion is speculative and the evidence remains frustratingly limited and incomplete. Perhaps a radicalized and committed Tsarnaev, unable to join the insurgencies against Russia in Dagestan or Chechnya, returned home to Boston and decided to wage jihad where he could rather than were he desired. It is a plausible narrative. However, given his potential involvement in a triple homicide in September 2011, and other evidence of his general dissatisfaction with life in America, possible depression and mental health issues, it may also be plausible that he used the jihadist rhetoric and imagery to cover over what was a deeper urge to violence driven by personal psychological issues, rather than political grievances. Unfortunately, we may never know. However, it remains a critical task to attempt to understand the process of "self-radicalization" for intelligence and law enforcement officials to effectively address the potential threat of "home grown" radical Islamic terrorism in the future.