Why did they leave Kiefer Sutherland's character alone?

They kill all the other boys besides Penn and Sutherland. The reason why Penn isn't killed is because he's in jail at that moment. But when Walken goes looking for Penn's brother, Sutherland is just there. He certainly didn't get killed at another moment because he shows up in the end at the court house.

So is there any reason for it, or did they just overlooked him (they meaning either the movie production, the real life criminals or both)? I thought it was a bit strange, he kills his own son but leaves a complete stranger alone. Maybe his role in real life was as limited as in the movie, but there is another one in the young crew that doesn't even have a line in the movie just like Sutherland and they do kill him.