Tamerlan Tsarnaev travelled to Russia in 2012 for a lengthy trip to the Russian republic of Dagestan
Continue reading the main story
-------------------------------------------------
Boston Bombs * Lone wolf * Q&A: Possible FBI failings * Chechnya - in 99 secondsWatch * Q&A: Interrogation
One of the Boston bomb suspects was added to a terrorism database 18 months ago at the request of the CIA, officials have told US media.
The FBI has already said it investigated Tamerlan Tsarnaev, 26, but had found no evidence of a threat.
Tsarnaev was killed during a police chase last week. His brother Dzhokhar, 19, is in custody over the bombs.
Three people were killed and more than 260 wounded when two devices exploded at the Boston Marathon on 15 April.
A US politician earlier confirmed the bombs were set off by remote-control.
But the devices were not sophisticated and apparently had to be triggered within a few streets of the explosives.
FBI 'not at fault'
Officials said Tamerlan Tsarnaev had been added to the Terrorist Identities Datamart Environment (Tide) on the request of the CIA.
The database contains as many as 745,000 entries, and individuals on that list are not necessarily on the so-called terrorist watch list.
Continue reading the main story
-------------------------------------------------
The Tsarnaev brothers * Sons of Chechen refugees from the troubled Caucasus region of southern Russia * Family is thought to have moved to the US in 2002 from Russian republic of Dagestan * They lived in the Massachusetts town of Cambridge, home to Harvard University * Dzhokhar, 19, was awarded a scholarship to pursue further education; he wanted to become a brain surgeon, according to his father * Tamerlan, 26, was an amateur boxer who had reportedly taken time off college to train for a competition; he described himself as a "very religious" non-drinker and