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This author draws on a lot of information from Russia sources. Russians, of course, have had a lot of problems with Chechin rebels who engaged in a prolonged and bloody separatist movement after the collapse of the Soviet Union. Chechnya is in the oil rich Caucasus region. In recent years Western agents have been very active in stirring up trouble for the Russians in nearby areas. See this, this, and this. Hence, I am inclined to give credibility to reports from these sources.
Thus, the Boston bombing event becomes curiouser and curiouser. I'm betting on the following scenario: the older brother, Tamerlan Tsarnaev, was recruited to a Chechen project by the CIA. He earned a lot of easy money participating in their "training sessions". Then he recruited his younger brother to participate in some projects to also earn money, and eventually they were set up as patsies in the Boston bombing event.