[mhking]

The person doing this is a whole lot more calculating than a spree or thrill killer. He's picking places, not people. He may well have already scouted these places before he started. Now that he's started, he goes to the place, sets up and shoots.

A "traditional" serial killer spaces out his crimes, if for nothing more than to prolong the "pleasure" he gets from it; a mass killer is more concerned with maximizing kills in a single location. This is much more calculating; it appears (at least to me) to be geared toward placing the general public in and around DC in genuine fear of going out in public; to "regular places" that people visit daily - school, the supermarket, the post office, department (or craft) stores, gas stations - I wouldn't be surprsied to see a church/synagogue or hospital next, and God forbid, perhaps even a daycare center before this thing ends.

[Catspaw]

He also seems to be picking places with or near parking lots--the only exception is the man mowing the lawn, but I don't know if there was a parking lot nearby. It'd be a place to sit and scope the place before the shootings, even long before the shootings.

I have a feeling that he has a list of possibilities and picks a place to shoot depending on what's the most available to him at that particular day and time. It's like a crime of opportunity with some preplanning.