Was the use of force justified in the following situation?
A 19-year-old woman was raped by two men. She subsequently invited them for a return date, at which time she killed one with a shotgun, while the other man fled.
The use of force was definitely not justified in this circumstance. This is simply a revenge killing.
The use of force is allowable to prevent things from happening, not to avenge them. A person may use force if they fear that something bad is going to happen to them, to their property, or to another person. But that is about something that is going to happen, not about something that has already happened.
In the case that you are describing, there is no imminent harm that is being prevented. You can't say she's killing the guy so that he won't rape someone else because there is no immediate prospect of him doing so.
The use of force in self-defense is only allowable when there is a bad thing that is likely to happen in the immediate future.
Under no circumstances was use of force justified in this situation; rather it reeks of vigilante justice. Use of force is justified only if there is an immediate danger to one's health or safety which can not be avoided by retreat; and the person using the force took no part in instigating the conflict. In the present situation, sufficient time had elapsed that there was no immediate threat to the young lady. Furthermore, she INVITED the second encounter, and obviously planned to kill one or both of them. Rather than justifiable, her actions constituted homicide with malice aforethought; the classic definition of first degree murder.