This is an awful story: Four young girls - ages 5 to 17 - found dead in their D.C. home, and their mother is charged with the murders. As if that wasn't enough, the bodies had been in the home, decomposing, for at least 15 days and possibly as long as several months. It's impossible to say why a parent would do something like this, but investigators now want to know how it could happen, and how no one noticed. Neighbors feel guilty, the mayor fired a handful of child welfare workers, and a social worker at the school one of the girls used to attend says she tried twice to get the city to check up on the kids. Obviously, in the end it's up to parents to protect their children, but when that fails, who's responsible for keeping kids safe? What happens when you report child abuse? And, how do you investigate such a sensitive issue? We'll talk with a former investigator and a school nurse about how they try to keep kids safe.