Yep.Fortunately, the crazies we have had here were just that: crazy. If they were stable and disciplined enough in their mission, two or three shooters with single shot, bolt action rifles and modest scopes could both terrorize the masses and cripple commerce for a long time.
other low risk yet high value targets are water supplies and sewer systems. it would not take much technical sophistication to compromise either without the use of a single bullet or bomb.
imagine 10% of Chicago without working sewers.