Ability, Opportunity, Manifest Intent, and Preclusion
Ability, Opportunity, Manifest Jeopardy, and Preclusion, are the cornerstones of any legally justifiable act of self-defense, especially using a weapon. In "Fundamentals of Defensive Shooting" by John Farnam, there is the best explanation of these concepts that I have found to date;
There are four elements to legitimate self defense, and they must all be present simultaneously in order for there to be a situation where deadly self-defensive actions are warranted. They are:
3. Manifest intent (imminent jeopardy)
An "ability" is simply an injurious capacity. It usually manifests itself in the form of a weapon of some sort, but not always. Serious injury can be inflicted by many individuals using no weapon at all. The person you applied deadly force against must have been "able" to kill you or inflict serious bodily harm. Threats alone do not suffice, unless he had the ability in hand to carry them out. If you were attacked by a person much larger than yourself, or by someone using martial arts techniques, or several individuals at the same time, you may reasonably conclude that he/they had the ability to seriously injure or kill you, even though they may have been technically "unarmed." Disparity in size, age, strength, sex, and the level of aggressiveness of the involved parties are all important matters when considering the element of "ability."
When considering the element of "opportunity," we must have a situation where this attacker, in addition to having an "ability," was also in a position to bring the destructive powers of his ability to bear effectively upon you. The question is, were you within the effective range of his weapon(s)? For example, a knife or bludgeon is harmless in the hands of someone standing twenty meters away from you, yet either can be deadly if the person is standing within arm's reach, or is several meters away but closing fast. A firearm, on the other hand, is considered deadly at any range.
You are in "imminent jeopardy" when the attacker unmistakably indicates, by words and/or actions, that it is his intention to kill or seriously injure you, and further, that he intends to do so at once. Your are not permitted to use deadly force to defend yourself against nebulous threats. The danger must be mortal and imminent. It must appear that the circumstances were sufficient to occasion the legitimate fears of a reasonable person, and that you acted under the influence of those fears, not in a spirit of vengeance or criminal assault. When a person has reasonable grounds for believing, and does in fact actually believe, that the danger of his being killed or seriously injured is imminent, he is permitted by law to act in self-defense based on those appearances even, if necessary, to the extent of using lethal force. This is true even if it turns out that the appearances were misleading and the person was thus honestly mistaken as to the real extent of the danger. It is for the jury to decide whether appearances of danger were sufficient so as to justify the defensive actions that were taken.
No one is expected to wait until they have absolute and incontrovertible knowledge that a threat is real. However, there must be an overt act coupled with that threat. The point is, it does no matter if your attacker's "weapon" later proves to be a toy, or non-functional, or unloaded. So long as, under the circumstances, you had good reason to believe (reasonable belief) that the weapon was real and functional and that he intended to use it to harm you forthwith, your defensive actions will likely be considered reasonable and appropriate. Remember, you will be judged only with regard to what you knew and reasonably believed to be true at the time. You will not be judged based upon facts and circumstances of which you had no cognizance.
"Intent" is, after all, a mental process. We therefore cannot perceive intent directly. We can only infer it from the person's actions and/or words. Accordingly, it is an error to say, "He was going to kill me." How do you know? Are you a prophet, or mind-reader?
The fact is that you don't know what was going through his mind. The correct way to phrase it is: "It looked as if he was going to kill me." That way, you correctly identify your motivating factor as his actions, which you can see, not his thoughts, which you cannot see.
Intent is not strictly necessary for imminent jeopardy to be present. You can, for example, be placed in lethal danger by an individual acting with extreme carelessness but who may have no specific intention of harming you.
"Preclusion" simply means that the other options were precluded. In other words, you used deadly force only as a last, desperate resort. The jury must be persuaded that, under the circumstances, you had no logical or reasonable alternative but to use deadly force to defend yourself. Generally, the more self-restraint you use, the more "reasonable" your actions will look. In fact, "self-restraint" is a key word, particularly if you used a firearm. It is desirable for the jury to see your actions as judicious, restrained, reasonable, and retrogressive. They should believe you made every reasonable effort to abate the situation, even including the use of non-lethal force, before finally resorting to the use of deadly force. Conversely, they should see your attacker's actions as precipitous, unwarranted, barbarous, and unconscionable.
Some states require preclusion as a component of legitimate self-defense. Some more liberally-inclined state legislatures have even based "mandatory retreat laws." In general, the require a person to retreat from an attack, rather than use deadly force to repel it, even when the person attacked otherwise has a right to be where he is. Generally, mandatory retreat laws apply to every situation,except when the victim is in his own home.
The outcome of criminal and civil court proceeding alike is often determined not so much by how a particular law is written, as it is by "courtroom poker." The winner is usually the one who can cause a jury to be sympathetic to his side, and preclusion is often the magic ingredient.
The decision to use deadly force always hinges upon a balance of two opposing imperatives: risk exposure and restraint.
Exposure to risk is, of course, inherent to all human activity. Risk cannot be entirely purged from any endeavor, but is must be identified, controlled, and minimized. Everyone is expected to expose themselves to some risk during the course of their daily activities. It is an understood condition of life. However, no one is expected or required to expose themselves to unreasonable or suicidal risk.
In any situation, as a person's risk exposure increases, he is permitted by law to take reasonable measure to reduce it, restraining himself from using deadly force until such a time as risk exposure has escalated, or is about to escalate, to unacceptable levels. At that point, deadly force may be employed if it is the only reasonable avenue through which the risk can be reduced.
ALWAYS CHECK WITH YOUR LOCAL, COUNTY AND STATE POLICE AGENCY'S REGARDING LAWS OF SELF-DEFENSE!