WASHINGTON - The mystery of how the Boston Marathon bombing suspects may have become radicalized and proficient enough as bomb makers to launch such a devastating attack earlier this month has deepened.
"Authorities now have legitimate reason to suspect that the older brother, Tamerlan, may have been associated with a larger terror organization," says a U.S. intelligence source.
And as federal law enforcement authorities question the parents of Tamerlan and Dzhokhar Tsarnaev and detain some of their friends, new information is emerging about a tactic terrorists allegedly are using to slip into the U.S. and to travel abroad.
WTOP has learned that the U.S. asylum system is a prime target for jihadist organizations because of the international acceptance that U.S. travel documents can provide.
"I know this from a very good source that al-Qaida is sending people into this country simply to get travel documents -- American travel documents -- so they can either operate here or abroad," says Robert Baer, a former CIA covert operative.
The alleged use of asylum loopholes by terrorists to get official country documents dates back more than 20 years.
The technique "was very popular in the 1990s, mainly in the U.K. Thousands of cases took place in Europe," Noman Benotman, a former terrorist and close associate of Osama bin Laden, tells WTOP.
According to U.S. intelligence officials, the leaders of the 19-man hijacking crew that attacked U.S. targets on 9/11 were a part of "The Hamburg Cell," which was based in Germany and lived and traveled using aliases.
The Tsarnaev brothers, ethnic Chechens from Russia who came to the United States about a decade ago with their parents, were granted asylum. Tamerlan Tsarnaev used that asylum status to become a permanent resident and obtained a green card.
Investigators say they now believe Tamerlan Tsarnaev became "radicalized" sometime between 2009 and 2010. Where it happened and who may have been involved in the process are among the questions investigators are asking, sources say.
In a statement, the FBI said Russian authorities told them in 2011 "that (Tamerlan Tsarnaev) 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."
WTOP also has learned the Russian FSB intelligence security service provided information on Tamerlan Tsarnaev -- including two possible dates of birth, his name in Cyrillic letters and a possible name variant -- in late September 2011.
That information was sent to CIA headquarters in October 2011 and formally passed to the National Counterterrorism Center, the Department of Homeland Security (DHS), the State Department and the FBI to be added to the Terrorist Identities Datamart Environment (TIDE) watchlisting system, according to a U.S. intelligence source.
Avoiding detection is the name of the game for terrorists seeking to get into the U.S., Baer says.
"DHS is quite concerned that people are dumping their documentation (and) coming across the border using aliases," he says. "There is a good strong suspicion, well-founded suspicion, that al-Qaida-like groups, Salafis, and militants -- whatever you want to call them -- are trying to get American permanent resident alien (APR) documents so they can travel."
Tamerlan Tsarnaev apparently had APR documents in 2012 when he went to Russia, and Benotman doubts that his movements were limited to that country.
"There's a big possibility that he went outside of Russia for training," he says.
Baer says having American travel documents would allow him to do that easily.
"You can't travel freely with, let's say, an Iraqi passport or a Syrian passport, but you can travel with American docs (SIC) anywhere in the world and they (U.S. authorities) don't know who these people are," he says.
According to U.S. Citizenship and Immigration Services, there are two ways of obtaining asylum in the U.S: the affirmative process and the defensive process. It's the affirmative process that worries many in the intelligence and law enforcement communities.
According to DHS documents, to obtain asylum through the affirmative process a person "must be physically present in the United States.
"You may apply for asylum status regardless of how you arrived in the United States or your current immigration status," the documents say.
The defensive process is mainly utilized by those trying to avoid deportation. Baer calls the U.S. asylum system "broken" and says immigration courts are rubber-stamping those seeking asylum.
"The FBI can't watch them all, but let's not blame the FBI for this," Baer says.
WTOP contacted the DHS multiple times to ask for clarity on the issue but did not receive a response. Several people in the agency all said only the DHS press office could respond.
The State Department also has not responded to a request for comment about its role in the asylum process.
Meanwhile, as authorities try to determine the degree of Dzhokhar Tsarnaev's involvement, a key question is whether he was a willing participant. Benotman says he thinks Tamerlan Tsarnaev recruited his younger brother.
"I think (Tamerlan Tsarnaev) was the one that organized everything -- during his mysterious trips to Russia," he says.
Benotman, who has denounced terrorism and is now a scholar with the Quilliam Foundation in London, was the leader of the Libyan Islamic Fighting Group and was present in Kandahar, Afghanistan, when the 9/11 attacks were planned in 2000.
Almost 12 years after 9/11, Benotman says, "I'm really concerned that (Tamerlan Tsarnaev) managed to be active, with no one noticing this."
Follow @WTOP on Twitter.
© 2013 WTOP. All Rights Reserved.