>> in a terrifying instant, the women, one is 84, and the other 96, go down. stunned passengers and bystanders race to the rescue. rose cohen, on her way to class, has just boarded. >> the younger sister, when she fell, the wheelchair came down with her. her head was off the edge of the curb, and she's laying on there. >> if you were there, what would you do? call 911? chase the mugger? or tend to the fallen victims. in this case with the bus full of people, it's all of the above. >> the bus driver already had his phone and he's screaming. everyone is running off the bus trying to see what happened. bystanders actually did run after the kid, but of course no e physically got him. >> the purse snatcher gets away in an accomplice's awaiting car. while people attend to the women. then, another choice has to be made. >> everyone is contemplating,