CNN CNN Special Report May 10, 2015 23:04:00
Homemade shrapnel intended to tear flesh and shatter bone. it is 2:37 p.m., about 4.5 hours since the start of the race. it's when a majority of runners are finishing. it is also go-time for the brothers, who round the corner onto the marathon route. their attack is timed to cause maximum damage. >> i always think of the families that just line that finish line. sometimes ten deep. and it is difficult to get by. >> that is where tamerlan positions himself. high school student sydney corcoran is to his left. >> it was a great vibe. everyone was just being nice and cheering them on like, "you ca...