Russian security services monitored Boston bombing suspect Tamerlan Tsarnaev during a five month visit he made to the North Caucasus region of Dagestan in 2011-2012, but found no reason to arrest him, a security source told AFP Monday.
The older of the two Tsarnaev brothers suspected of setting off the Boston marathon bombs, 26-year-old Tamerlan was shot and killed Friday by US police, while his younger brother Dzhokhar was wounded and is in custody.
Tsarnaev travelled to Russia's southern region of Dagestan, where he had previously lived, in late 2011, staying for a total of five months and 13 days, said a security source involved in tracking extremist activity in the region.
"Security services came across Tamerlan four times" in course of his visit, he told AFP.
"They were monitoring another young man, suspected of connections with the Islamist insurgency, and Tamerlan was seen with him."
"But then the young man disappeared from view of the security services, and Tamerlan was no longer seen either," the source added. "He left Dagestan in June of last year. Nothing was seen for which he could be detained or charged."
Since it was known that Tamerlan came from the United States, Russia asked the FBI for information about him, once at the end of 2011, and once several months after he left, in November 2012, the source said.
The FBI said Friday that a request from an unidentified foreign government for information about Tamerlan Tsarnaev came as he was "prepared to leave the United States for travel to the country's region to join unspecified underground groups."
Dagestan is the most restive of the North Caucasus regions, a mountainous territory in the south with a mostly Muslim population and an ongoing Islamist, anti-Kremlin insurgency.
However the local branch of the main Caucasus Islamist group Caucasus Emirate denied on the weekend that it had any involvement in the Boston blasts, which killed three people and wounded 180.