text: Most states have a penal code section for justifiable homicide.  You would be commiting homicide, you would just have to explain why you did it.  I am sure the kid would be a witness for you. Officers commit justifiable homicide when they kill someone in an officer involved shooting incident.  The issue you have however, is you're not a cop, therein you would have a harder time justifying why you used the amount of force you used.  I say, "you would have a harder time," because police officers are in use of force situations daily, therein, they deal with the use of force more often and can articulate their reasons for shooting a bad guy.  Nonetheless, even the officer would be represented by extremely well-trained council.