runners and there's so much momentum in that herd, and everyone stopped. >> there was a little bit of a dead silence right after it happened. >> there weren't screams for help. there weren't people crying. everybody had their mouths kind of open, like they wanted to say something, to scream, and nothing was coming out. their eyes were wide open and they were just in faraway trances, as though they were in complete shock. >> chris and kayla, natalie and her dad were all safe. hundreds of others were not as lucky. >> it was a process not fast enough for me to say, wait a minute, that guy's leg is gone, that woman doesn't have a leg. where is her arm? >> it was scattered. it felt like 30 feet across just of carnage, blood, body parts. >> then, what started as a race to a finish became a desperate race against time to save the lives of the gravely wounded.