Self Defense as an Affirmative Defense

In which states in the US is self defense an affirmative defense against a charge that involves killing a human being (i.e. murder, or manslaughter, or whichever other charge fits the bill)?

Of course; what else could it be?

You might be arrested and then have to prove in court that you had no choice but to kill the attacker. A jury may have to decide if you acted in self defense or not.

“Affirmative Defense” meaning a defense that’s held to be true in all cases, or perhaps doesn’t need to be demonstrated is a better phrasing?

An affirmative defense is a defense in which the defendant must prove some circumstance that causes him to not be guilty. In a regular defense, it is the prosecutor’s job to prove the defendant guilty; the defendant does not have to prove anything. In other words, an affirmative defense shifts the burden of proof from the prosecutor to the defendant.

As far as I know, self-defense is an affirmative defense everywhere.

I stand corrected, thanx.

http://www.nolo.com/legal-encyclopedia/burdens-proof-criminal-cases.html

The most well-known affirmative defense is self-defense. It generally entails the defendant acknowledging that she committed the alleged act, but arguing that it appeared to be necessary in order to defend herself from harm. An example is fighting off a mugger.

Some states may require defendants to prove self-defense by a “preponderance of the evidence,” while others require them to simply raise a plausible basis for it, and the prosecution to disprove it beyond a reasonable doubt.

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So - in those states although self-defense is formally “affirmative”, it does not have to be proven by the defense for acquittal.

This site says that the “others” above are 49 states. Only in one - Ohio - the defendants have to prove self-defense by “preponderance of the evidence”.

Obviously Texas allows self-defense as a reason, but if the OP doesn’t mind an additional question:

Do any states besides Texas allow deadly force to protect property? (i.e. prevent theft, and/or prevent someone from fleeing with property) I think Montana allows it to prevent trespassing, but Texas does not (there needs to be a clear threat of theft, not just “he was on my land”).

I’ll leave it to the legal experts to verify my interpretation, but the statutes here regarding property seem pretty clear.

Here’s the wording. Texas Penal Code 9.42:
*A person is justified in using deadly force against another to protect land or tangible, movable property:

(1) if he would be justified in using force against the other under Section 9.41*; and
(2) when and to the degree he reasonably believes the deadly force is immediately necessary:
(A) to prevent the other’s imminent commission of arson, burglary, robbery, aggravated robbery, theft during the nighttime, or criminal mischief during the nighttime; or
(B) to prevent the other who is fleeing immediately after committing burglary, robbery, aggravated robbery, or theft during the nighttime from escaping with the property; and
(3) he reasonably believes that:
(A) the land or property cannot be protected or recovered by any other means; or
(B) the use of force other than deadly force to protect or recover the land or property would expose the actor or another to a substantial risk of death or serious bodily injury.
*

*statute about deadly force to avoid being dispossessed of your property

I think it should be emphasized that you must admit to the act in order to claim the defense. In other words, you cannot argue, “I didn’t do it, but if I did, it was justified.” Your argument has to be, “I killed him, and I was justified in doing so.” You have to admit it, or the argument is not available to you.

The phrase “affirmative defense” means different things in different contexts. For example, some defenses are designated affirmative defenses because the defendant must plead them or has an initial burden of producing evidence for them even though the other party has the ultimate burden of proof. I’m assuming the OP is asking about which jurisdictions put the ultimate burden of proof for self-defense on the defendant.

As of 1984, only Ohio did not require the prosecution to disprove self-defense once the defense was raised. I believe Ohio now has a semi-complicated burden-shifting framework, but that in at least some circumstances the defendant still has the burden of proof for self-defense.

If the OP is asking where self-defense is not a defense at all, the answer is nowhere in the US.