Within each of us is a natural law that tells us what we ought to do when faced with a clear moral choice. For example, if we see someone in peril our choice is to save that person. Now, whether or not we do it is another matter, but clearly we know what we ought to do.
The key word here is ought. This natural law has been brilliantly discussed by C.S. Lewis in the book, "Mere Christianity." Lewis goes on to argue that the source of this natural law is God. Now in the case of the Newtown tragedy, the question is, what ought we do?