families with small children, including the richards, with 11-year-old henry, 6-year-old jane, and 8-year-old martin. it's now 2:50 p.m. dzhokhar raising a phone to his ear. the plan is now in motion. >> what the hell was that? >> tamerlan detonates the first bomb. >> oh, my god, something blew up. >> in the ensuing chaos, dzhokhar walks quickly away from his backpack. he leaves it on the ground, right near 8-year-old martin richard. behind the richards in a blue sweater is 23-year-old lingzi lu. >> she walks into frame right before that first bomb goes off.