The younger brother on the loose, Dzhokhar, was a star student at Cambridge Rindge & Latin High School, graduating in 2011. He was also a high school wrestler, and became a naturalized U.S. citizen Sept. 11 of last year. Classmates who knew him in high school told the Boston Globe he was friendly but not close to anyone. Students who knew him at UMass-Dartmouth also said he tended to keep to himself and did not talk about his Russian background. His father, contacted by the Russian news agency Interfax, said he was a medical student. But UMass officials said he was studying marine biology.