A couple hundred will buy you a nice ruger in .223 for a few bucks more you add a bi-pod and good quality scope.
With this simple, buy it anywhere hardware I (or just about anybody with a little patients) could have the average 10yr old getting 5" groups @ 300yds in about 1/2 an hour.
This isn't brain surgery.
The guy isn't selecting targets. He’s taking targets of opportunity. Find a spot with good cover and an exit, pick your target area (so you know the exact range already) and shoot the first unfortunate soul who walks into your sights.
The sad thing is it makes him pretty damn hard to catch. About the only way he could be caught is if-
1. He’s a solid nut-job (my guess). In which case he's doing it for attention or fame, whatever. Anyway he'll get bored and do something to make the hunt for him more interesting (the tarot card thing, the phone number, and the letter) eventually leading the cops to him.
2. Pure luck, some body stumbles upon him, his car breaks down, something like that.
3. One of his accomplices (or somebody he mouthed off to) turn him in. My bet is he has at least one guy working with him. A spotter to watch out for him while he's in the scope, maybe a lookout in a second vehicle.
If it turns out it's an organized terrorist thing this could be going on a long time. Hopefully though this Tacoma thing will pan out and they will get soon