Interesting theory, but some of these killings don't fit the car dealership/gas station/Michaels scenario. School shooting, bench sitter(in front of a Post Office), Montgomery & Prince William Co. isn't the area that would be associated with support of oil companies or hostile to the environmental movement.
It might make sense, however, if it is a couple of ecowacko's who grew up in the Montgomery Co. area and had a grudge against their hometown area.
Everyone IMHO is looking at this situation with the binoculars turned backwards, that is, studying the victims.
This sniper doesn't care who he shoots. He is 90% concerned with setting up an isolated shoot site in close range of normal human activity, with a near perfect isolated escape route. Then and only then does he select a random victim who walks into his crosshairs.
Look for the slick escape routes and remote shoot sites with a line of fire to gas stations etc. That's the way to look for this guy, from the escape route end.