During this turmoil, his mother encouraged him to turn to Islam. "I told Tamerlan that we are Muslim, and we are not practicing our religion, and how can we call ourselves Muslims?" Mrs. Tsarnaeva said. "And that's how Tamerlan started reading about Islam, and he started praying, and he got more and more and more into his religion."

Tamerlan delved deeply into religion at the urging of his mother, who feared he was slipping into a life of marijuana, girls and alcohol. Tamerlan quit drinking and smoking, gave up boxing because he thought it was in opposition to his religion, and began pushing the rest of his family to pursue stricter ways, his mother recalled. "You know how Islam has changed me," he told her.

People who knew him say Tamerlan would express outrage when he perceived a religious slight and was critical of Muslim immigrants' efforts to assimilate in the U.S.

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