There is a book that explores this subject reasonably well.
Below is an excerpt from Mark Fuhrman’s book, The Murder Business.
A small number of these cases explode into national obsessions as a mass media feeding frenzy ensues over their stories. Typically, the victims are female. Without exception, they are white and very pretty. In a ghoulish moment, American Murder meets American Idol, as America chooses its prettiest corpse, onto whom our collective horror is projected.
It begins with a photograph that quickly becomes iconic in our culture, a name we adopt into our national conversation as if we were speaking of someone we all knew, JonBenet, Caylee, Stacy Peterson, Laci Peterson.