Aiming for the head is most likely. For reference, a military M16 is considered within spec if it can produce a 4 minute-of-angle group from a prone supported position (but aimed and fired by a human, not fixed in a gun sled). At 200 yards, that would be a circle of around 8 inches. However pretty much any hit with a rifle bullet within that circle is likely to be lethal if it's centered on the head...

Anyway, the point is that it's really not a difficult shot at all, and only requires very rudimentary training that is readily available to anyone who can make a few trips to the range.

I'm not sure that most people are disciplined enough to make that shot all the same. I don't know anything about the shooter in particular though. Mostly in that from the center of the head to the neck is still a bit away. It could just as easily have missed altogether.