I still have trouble believing this to be a motiveless crime, which is why I've long thought that the answer must be much closer to home; I suppose it just disturbs my sense of order that a person could have left the highway, found the road and the two girls, and shot them down for very little or no reason at all. It all seemed a little too pat that the POI sketch would be of a Native American - a "bad Indian," one who, as in a stereotype, appeared stealthily, killed, then disappeared almost without a trace save for the one sighting which led to the sketch.
But stranger things have happened, and my notion of an ordered universe may, too, be an illusion.