The law of self-defense allows people to use force, and sometimes deadly force, to defend themselves from an imminent threat of harm. In most states and circumstances, if the defendant's fear and the amount of force used are reasonable, he'll "walk." But what if a defendant uses deadly force, and either the fear or the amount of force is unreasonable? The doctrine of imperfect self-defense may apply, by negating the element of malice and reducing a murder charge to manslaughter. (See Homicide: Murder and Manslaughter.) In that way, imperfect self-defense is a "partial" defense.
Many states don't recognize the doctrine of imperfect self-defense. In those that do, court decisions have developed and refined it.
(For related concepts, see Defense of Others and Self-Defense.)
Unlike "perfect" self-defense, which is available for most violent crimes, imperfect self-defense applies only to murder and attempted-murder charges. It negates only the type of malice required to prove murder; it doesn't apply to other crimes, even those that have malice as an element. For instance, even though the crime of mayhem often includes a malice element, imperfect self-defense doesn't apply to it.
In the states that recognize it, imperfect self-defense typically applies where a defendant kills someone pursuant to an actual, but unreasonable belief that:
If there is evidence that the defendant actually believed in the need for self-defense, both imperfect and perfect self-defense could apply. Which defense is successful depends on whether the defendant's belief was reasonable. It's for the jury to ultimately determine the reasonableness of the belief.
Example: Oscar, who lives alone, awakens in the middle of the night in his bedroom and hears someone moving around in the next room. He hears footsteps coming toward his bedroom door and gets his gun from the nightstand. As he sees the doorknob begin to turn, he starts firing, killing the person on the other side of the door. Oscar doesn't qualify for "perfect" self-defense if he didn't reasonably believe that he faced an imminent threat of death or great bodily injury when he started shooting. Firing through the door without knowing who was on the other side may have been unreasonable. As a backup to self-defense, Oscar could argue imperfect self-defense in order to reduce the murder charge he faces to manslaughter.
Note, however, that the outcome of a case like Oscar's will depend in part on the law in the state in question. For instance, variations on the "castle doctrine" may provide a complete defense in somewhat similar cases. (See "Stand Your Ground": New Trends in Self-Defense Law and Self-Defense Laws.)
In some states, imperfect self-defense applies only if the defendant would have had a perfect self-defense claim had she not acted on an unreasonable belief about the need for force or the amount of force necessary. In other states, imperfect self-defense may apply in additional circumstances—for example, where the defendant provoked the conflict, didn't fulfill a duty to retreat, or used excessive force.
Provocation. If the defendant creates a situation where the victim is legally justified in using force—say, by first attacking the victim—then imperfect self-defense usually doesn't apply. But consider the following example.
Example: A wheelchair-bound defendant invited his cousin to meet him and several others in an alley. When the cousin arrived, the defendant confronted him about a past sexual attack on the defendant's brother. After the cousin lunged at and started choking him, the defendant pulled out a gun and shot the cousin several times, killing him. Because the cousin's use of force was unreasonable, the defendant could claim imperfect self-defense, even though he set in motion the chain of events leading to the cousin's initial attack. (People v. Vasquez, 136 Cal. App.4th 1176 (2006).)
No retreat. Imperfect self-defense may be available if the law requires someone to retreat before using force. In a duty-to-retreat state, a defendant who didn't retreat, but otherwise reasonably acted in self-defense might have to settle for imperfect—rather than perfect—self-defense.
Victims of Abuse. Imperfect self-defense often becomes an issue in cases where the victim has abused the defendant over time. Depending on the state and the facts, perfect self-defense may even apply. For instance, a history of trauma may be relevant to the reasonableness of the defendant's belief in the need to defend herself.
Even in those states where imperfect self-defense can be a viable claim, its requirements vary. And there may be limitations to the doctrine not covered in this article. It's important to seek the advice of an experienced attorney in any criminal case. An attorney in your state will be best able to explain the law and advise you as to how it applies to your case.