released this week was very, very careful to say look, we know he used weapons of mass ru people, and that s enough to give him the death penalty. reporter: to build the case and find the answers, hundreds of federal investigators are now working around the clock, digging through debris, analyzing bits of bombs in one of the nation s largest terrorist investigations since 9/11. neighborhoods like this one across boston are being visited by the fbi. this man says five fbi agents showed up at his door to question his son about tweets sent to the younger brother. and on the college campus where dzhokhar went to school, friends there tell cnn they too have been visited by the fbi. up-front next, breaking news. we ll hear about the terrifying ride through boston. there is a lot of news reporter: leads are still
because people knew he was a boxer and he had more of a reserved personality to him. but if you went up to him, he talks to you right back and he was very friendly. reporter: but were there any clues of the violence to come? he never expressed any desires to harm people. they did respect life at one point. they were friendly. reporter: after high school tamerlan attended bunker hill community college, studying accounting. until 2008, when he left college. but he continued to pursue his dream. good? mm-hmm. reporter: boxing trainer eddie bishop met tamerlan at a tournament. he was a fighter that had a lot of skill and a lot of a lot of ability. reporter: but bishop questioned whether tamerlan could ever become a boxing champ. he had all the skill, but he lacked the heart, the fundamental ingredient to make you a champion. reporter: the tsarnaev family is from war-torn chechnya and came here to the u.s. more than ten years ago. dzhokhar came first, and then later hi