This is definitely somebody who is determined to frighten the populace, either for the sheer physical rush he must get from having the "power" of life and death over anybody he targets and controlling the movements of so many people, or else his purpose may be to frighten people into not leaving their homes, thereby disrupting the economy.
This could very well be an organized Islamist terrorist campaign, some Islamist freaks acting on their own initiative, or it could also be a homegrown nut a la the Unabomber.
Either way, this ain't no Agatha Christie novel, and these people (I happen to believe there are at least 2 involved) are going to screw up sooner or later. I think they've already started to screw up in that they haven't struck the last two victims in the head.
I agree in theory with the people on this thread who are saying that it doesn't take a rocket scientist to be a good marksman, but I also think that killing another person does require a certain amount of skill and discipline, because you have to marry the basics of shooting with the will to kill. I doubt any of our FR sports hunters could calmly and accurately fire on a human target they know to be innocent.
IMO, these snipers do not view their targets as human beings, or else they have convinced themselves that the victims are "guilty" of something and therefore deserve to die. For whatever reason, they have the will to kill innocent human beings, which I don't think the FReepers most experienced with firearms and hunting possess.