More likely two twenty something misfits who have some hunting experience. They are sniper wannabees. They have seen the movie "Sniper" (Great movie)too many times. If they were military they would be using a deer rifle, they would be firing from a longer range, and they probably wouldnt be fleeing the area by van. They would merely lie in place or crawl away (in plain sight). Each shooting had a wooded park area nearby.
BTW, the cop was dealing with an accident on the expressway and he was 50 yards from the shooting victim, not the shooter.