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By Richard Valdmanis BOSTON (Reuters) - The older brother of convicted Boston Marathon bomber Dzhokhar Tsarnaev was transformed from a heavy drinker and drugs user into someone obsessed with Islam after returning from a trip to Russia in 2012, witnesses said on Tuesday. The 21-year-old ethnic Chechen was convicted this month of killing three people and injuring 264 in the bombing, and shooting dead a police officer three days later alongside the older brother, Tamerlan. Rogerio Franca, who lived near the Tsarnaev family in Cambridge, Massachusetts, told jurors Tamerlan was a partier before his trip to Russia but transformed into someone more closely resembling a devout Muslim when he returned. "Most of the time he was drunk, most of the time he was high," Franca said of Tamerlan before his trip.