Boston: With one suspect dead and the other lying seriously wounded in a hospital, the FBI investigators are reviewing the suspected Boston Marathon bombers` motives and a visit made by one of them to Muslim-dominated Chechnya and Dagestan republics in the Russia`s north Caucasus region.
26-year-old Tamerlan Tsarnaev, who was killed in clashes with police in Watertown on Friday, travelled to Russia from Boston several times in recent years, according to US officials who have reviewed his passport file.
He spent six months in Dagestan in 2012 and analysts said that sojourn might have marked a crucial step in his alleged path toward the bombings, according to the New York Times.
Both the suspects were brothers from Chechnya, which has witnessed deadly bombings carried out by Islamic rebels.
The FBI in 2011 interviewed Tsarnaev, suspected of being behind the deadly Boston blasts that claimed three lives and injured over 180, at the request of a foreign government (now acknowledged by officials to be Russia) that suspected he might have ties to extremist groups with links to al Qaeda.
The senior law enforcement official said the Russians feared he could be a risk, and "they had something on him and were concerned about him, and him travelling to their region."
Chechen extremists pose a greater threat to Russia than they do to the US, counter-terrorism specialists say, though some of the groups have had ties to al Qaeda, the paper said.
The US investigative agents apparently let him out of their sights after not detecting any terrorist activity.
"The request (by the foreign government) stated that it was based on information that he was a follower of radical Islam and a strong believer," the FBI said.
Agents also interviewed Tsarnaev`s family members, the FBI said, but did not detect terrorist activity.
"The FBI did not find any terrorism activity, domestic or foreign, and those results were provided to the foreign government in the summer of 2011," it said in a statement.
Tsarnaev`s uncle, Alvi Tsarnaev, told the Boston Globe that the nephew visited his father in the restive Russian province of Dagestan, which neighbours war-torn Chechnya.
But Alvi said he did not know who else his nephew may have been involved with while he was overseas.
One month after Tsarnaev returned from Dagestan and Chechnya to the United States, a YouTube page that appeared to belong to him was created and featured multiple jihadist videos that he had endorsed in the past six months.
One video featured the preaching of Abdul al-Hamid al-Juhani, an important ideologue for al Qaeda in Chechnya and the Caucases; another focused on Feiz Mohammad, an extremist Salafi Lebanese preacher.
He also created a playlist of songs by a Russian musical artist, Timur Mucuraev, one of which promoted jihad, according to the SITE Intelligence Group, which monitors jihadist sites.
Meanwhile, the Kavkaz Centre, an Islamic Chechen Internet agency believed to be the mouthpiece for Chechen Islamists, has dubbed Dzhokhar and Tsarnaev as "strange terrorists”, because "one dreamed of career and money, and the second to play for America at the Olympics", according to the USA Today.
The revelation about questioning of one of the suspects has raised new questions about whether the Marathon attack could have been prevented.
Chairman of the House Homeland Security Committee Michael McCaul said on Friday that information that Tsarnaev had been interviewed by the FBI in the past was disturbing.
"It`s new information to me and it`s very disturbing that he`s on the FBI`s radar screen," McCaul said.
"But if he was on the radar and they let him out of their sights, then that`s an issue, certainly, for me," McCaul said.
Tsarnaev`s brother and alleged co-conspirator Dzhokhar Tsarnaev, 19, was captured by police on Friday in Watertown. He is hospitalised "serious but stable" condition.
Kevin R Brock, a former senior FBI and counter-terrorism official, said, "It`s a key thread for investigators and the intelligence community to pull on."