I'm not being critical of the parents at all, but maybe the one thing they might have tried is the two older brothers. A little, "Go have a talk with him, man to man" if you know what I mean.
I agree with that approach. In fact, the dad called this kid over to talk with him man to man over the issue. That is when the kid shot and killed him.
I do believe the presence and activity of a male is a good thing. I told my daughter's fiance the following: "I know you will fight. I know you will have some "interesting" fights and will feel like there is no love left. When that happens, if she comes "home to us" we will help her settle down and send her back to her REAL "home," which is with you. If there is another woman, she can come home and stay...... but if you ever hit her, I will either kill you or make you wish you were dead. I am an old man now and I am a Christian, but when it comes to my daughter, I forget all about Jesus and turning the other cheek and I know how to equalize the age thing. I don't think that will ever happen, and I love you like you are my son. But you never hit my daughter, cause the day you do that, she is not FIRST your wife and SECOND my daughter. Then she reverts back to the daughter that I am bound to protect."
He said "I would die for your daughter, and if I ever hit her, someone SHOULD kill me." which, of course, is what any future father in law wants to hear.