My guess is that it is el Qaeda and that they are shooting at suburban locations (the heart of America) where they can park above and far enough away to wait for an opportunity and then get away fast. Strip malls and parking lots are open fields. These guys are simply hunting and killing American people with impugnity--letting us know that we are powerless to stop them.
That's what they want everybody to think, but they ain't gettin' on the hwy. Not until they're done with the evasion and heading home.