What did the Russian Security Services do or not do while Tamerlan was in their country? Is it possible that the Russians allowed Tamerlan to return to the USA in their expectations that eventually he would commit Ismalic terrorism?
Reminds me of the scene in ‘Skyfall’ when Bond asked Patrice “Where’s the list?” before Patrice fell from a skyscraper to his death. It appears that the same will be asked of the Teen Terrorist...