By Tim Lister and Paul Cruickshank
Tamerlan Tsarnaev appears to have become increasingly radical in ithe last three or four years, according to an analysis of his social media accounts and the accounts of family members. But there is so far no evidence of active association with international jihadist groups.
In August 2012, soon after returning from a long visit to Russia, Tsarnaev created a YouTube channel with links to a number of videos.
Two videos under a category labeled "Terrorists" were deleted. It's not clear when or by whom. But analysis by CNN and the SITE Intelligence Institute has uncovered a screen grab from one of those videos. It features members of the group Imarat Kavkaz - identifiable by the logo on their shirts. Imarat Kavkaz is the most potent militant Islamist group in Russia's North Caucasus region - which includes Chechnya and Dagestan.
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