Strange that the first reflex of people is revenge even more than sadness. We're not in the middle age anymore and we live in "civilizated" countries. No need to do the same as them, to be as monstruous as them.
Absolutely a tragic story and you wonder how sick people like this can be around in the world today.
Just give these two people five minutes alone with the parents of these two girls. How could they do something like this to girls that were so young, and had so much more life to live.