Detectives in Boston are looking further afield as they piece together their case against Marathon suspect Dzohkhar Tsarnaev.
The uncle of Boston bombing suspect Tamerlan Tsarnaev described his recent visit to Dagestan in Russia and his great shock at the attacks.
Both men were enrolled in a school in Dagestan, a neighbouring region that was drawn into Chechnya's violence during the 1990s.
On Wednesday 17th April, two days after the Marathon, he tweeted that he was "stress free":
I'm a stress free kind of guy
On Tuesday 16th April, a day after the bombing, he posted the following messages:
Ain't no love in the heart of the city, stay safe people
So then I says to him, I says, relax bro my beard is not loaded
The Boston bombing suspect who is still on the run became a US citizen on September 11 last year, according to documents obtained by NBC News.
Dzhokhar Tsarnaev, 19, had a Massachusetts driver’s license and was living in Cambridge, near Boston.
Deceased Boston Marathon bombing suspect Tamerlan Tsarnaev reportedly told a Massachusetts newspaper in 2004: "I like the USA".
Speaking after winning a novice boxing match, Tsarnaev told the Lowell Sun: "I like the USA ... America has a lot of jobs. That's something Russia doesn't have. You have a chance to make money here if you are willing to work."
According to the 2004 article, Tsarnaev grew up in Grozny, Chechnya, and moved to the US with his family in 2003.
It is thought that the brothers who have been identified as suspects in the Boston marathon bombing, Dzhokhar and Tamerlan Tsarnaev, are from a Russian region near Chechnya, having moved to the US around 10 years ago.
ITV News correspondent Lewis Vaughan Jones reports:
A Chechen leader said the Tsarnaev brothers' "root of evil" is in the United States, not in Chechnya.
"The root of evil should be looked for in the United States," said Ramzan Kadyrov, the Head of the Chechen Republic.
"(The brothers) grew up and studied in the United States and their attitudes and beliefs were formed there. Any attempt to make a connection between Chechnya and the Tsarnaevs is in vain," he added in a post in the Instagram website.
Deceased Boston Marathon bombing suspect Tamerlan Tsarnaev spent six months overseas last year, travel documents obtained by NBC 4 New York reportedly show.
Tsarnaev flew from John F. Kennedy Airport in New York on 12 January, 2012, for Sheremetyevo, Russia, and returned to JFK on 17 July, the local NBC station reported.
The documents are said to show that the suspect was born on Oct. 21, 1986 and first entered the US on July 19, 2003.
Investigators hope to find out if he received any terror training while he was overseas.
There is no record that his brother Dzhokhar Tsarnaev, who is still at large, left the US, the report adds.
Boston bombing suspect Dzhokhar Tsarnaev posted links to Islamic websites and others calling for Chechen independence on what appears to be his page on a Russian language social networking site.
Abusive comments in Russian and English have flooding onto Tsarnaev's page on VK, a Russian-language social media site. VK has over 200 million users and is particularly popular in Eastern Europe.
On the site, Tsarnaev identifies himself as a 2011 graduate of Cambridge Rindge and Latin School, a public school in Cambridge, Massachusetts.
It says he went to primary school in Makhachkala, capital of Dagestan, a province in Russia that borders Chechnya, and lists his languages as English, Russian and Chechen.
His "World view" is listed as "Islam" and his "Personal priority" is "career and money".
He has posted links to videos of fighters in the Syrian civil war and to Islamic web pages with titles like "Salamworld, my religion is Islam" and "There is no God but Allah, let that ring out in our hearts".
Russia condemns all "terrorists" regardless of their nationality, President Vladimir Putin's spokesman said on Friday after US police shot dead a terror suspect who once lived in Russia.
"They all deserve to be rejected," spokesman Dmitry Peskov said, adding that Russia was awaiting official information from the US on the dead man and a suspected accomplice.
Boston bombing suspect Dzhokhar Tsarnaev attended a school in Makhachkala, the capital of Dagestan, in 2001, Reuters reported.
The school register pictured above names Tsarnaev as a pupil - number 11 on the list.
The registry states Tsarnaev is Chechen, entered the school in 2001, studied in the first grade and arrived from Kyrgyzstan.