Affirmative Defenses in Criminal Cases

Affirmative defenses differ from state to state. And, the burden of proof for the defendant in proving an affirmative defense also differs.

By , Attorney · Seattle University School of Law

Sometimes a criminal defendant is entitled to acquittal even though the prosecution has proven every element of the charged offense. This happens when the defendant has successfully raised and the jury has accepted an "affirmative defense" that operates by law to exonerate him. Common affirmative defenses include a plea of insanity, self-defense, mistake of fact, intoxication (in some situations), and the running of the statute of limitations (the time period, starting when the crime occurred, during which a prosecution must begin).

Affirmative defenses are controversial and involve fundamental constitutional rights. This article describes affirmative defenses, why they exist, and how they function.

Defending Against a Criminal Charge: Disputing the Prosecution's Case

In every criminal prosecution, the prosecutor must prove, beyond a reasonable doubt, every "element" of the charged offense. Elements of a crime are the components of conduct, intent or mental state, and harm that together make something a crime.

For example, murder is the intentional killing of a human being by another human being. The basic elements are:

  • the killing of a human being
  • by another human being
  • who intended to kill the victim.
So, a chef who unknowingly serves tainted food to a patron that leads to the patron's death has not committed murder (though they may have violated other laws). The chef did not intend to kill the patron and the required mental state to support a murder conviction cannot be proven.

In a criminal trial, the prosecution puts on witnesses and introduces evidence to support every element of the charged offense. As you no doubt know, defendants try to discredit or chip away at this evidence, mainly through objections to its admission and cross-examination, and by introducing evidence of their own. When a defendant obtains an acquittal, it's because this attack has resulted in the judge or jury being unable to say that the prosecution has proved every element of the crime beyond a reasonable doubt. In some cases, the defense wins without putting on any witnesses of its own or introducing any evidence—the jury simply finds that the prosecution didn't meet its burden.

Examples of attacking what's known as "the prosecutor's case in chief" include challenging an eyewitness on the accuracy of her reported observations, uncovering a witness's bias through cross-examination, putting on an expert to dispute the prosecution's expert, and so on.

Defending Against a Criminal Charge: Using an Affirmative Defense

The defense strategy described just above isn't the only way a criminal defendant can obtain an acquittal. Instead of (or in addition to) trying to defeat the prosecutor's goal of proving every element, a defendant can also introduce evidence of his own that, if believed by the jury, will defeat the charge. The word "affirmative" in the term refers to the requirement that the defendant prove the defense, as opposed to negating the prosecution's evidence of an element of the crime.

An affirmative defense operates to prevent conviction even when the prosecutor has proof beyond a reasonable doubt as to every element of the crime. For example, consider again the elements that the state must prove when charging murder (that a human died, killed by another human, who intended to do so). Now imagine a claim of self-defense—the defendant says that he shot the victim only after the victim attacked him. There is no doubt that a human died, killed by another human who intended to do so. But if the jury believes the defendant's claim, he will escape conviction.

George Zimmerman's Affirmative Defense in the Trayvon Martin Murder Trial

The attorney for Zimmerman, who was on trial in Florida for shooting the unarmed teen Trayvon Martin, planned to offer evidence that Martin attacked Zimmerman and that Zimmerman shot Martin in self-defense. This affirmative defense has a unique feature in Florida: Under that state's "stand-your-ground" law, a person may use deadly force when attacked if he reasonably believes it necessary to protect himself from death or great bodily harm.

How Defendants Prove Affirmative Defenses

An affirmative defense of self-defense, or any other affirmative defense, doesn't just present itself. While a criminal defendant may decide to offer no evidence during trial, hoping the prosecution will fail to meet its burden, this approach won't work if the defendant has an affirmative defense. The defendant must offer proof at trial supporting the affirmative defense, meeting the standard of proof set by state law (usually a preponderance of the evidence, which is a lesser standard than the prosecution's). If the jury concludes that, for example, a preponderance of the evidence supports the defendant's claim of self-defense, it must acquit.

Some commentators have criticized imposing upon a criminal defendant a proof standard higher than just raising a reasonable doubt as to the prosecution's case. For example, the Model Penal Code developed by the American Law Institute proposes that a criminal defendant's evidence supporting his affirmative defense need only raise a reasonable doubt as to culpability. But the U.S. Supreme Court has upheld state laws requiring defendants to prove affirmative defenses.

Defendants usually offer an affirmative defense only when they have more or less conceded that the prosecution can prove all of the elements of the crime. (A vigorous disputing of the prosecutor's case in chief may not go down too well when the defendant proceeds to offer an affirmative defense. There's a reason why the old line, taken from a closing argument, elicits laughter: "Ladies and gentlemen, you must acquit! My client wasn't there! If he was there, he didn't mean to do it! If he was there and meant to do it, he's crazy!")

Creating Affirmative Defenses from Elements of the Crime

Having an affirmative defense available to the defense is usually a good thing—if the defendant is mentally incapable of forming the required criminal intent, his attorney will be eager to present that evidence. But in a legislative sleight of hand, a few states have created affirmative defenses that actually put the defendant at a disadvantage. Here's the ploy: to make it easier to obtain a conviction (and to please a political constituency), legislatures at times excise a single aspect from a crime (for which the prosecution previously bore the burden of proof) and recharacterize it as an affirmative defense, requiring the defendant to prove it. For example, some states have shifted to defendants the burden of proving their mental state where it supports an affirmative defense

Legislatures are constrained by the Constitution, however, to some extent. It would be unconstitutional for a state to remove an element such as intent and call it an affirmative defense that the defendant had to disprove. But, a state may constitutionally turn a former element of a crime into an affirmative defense if it can still punish the crime regardless of the affirmative defense, by proving the remaining elements. In some states, such as New York, a person may be convicted of second degree murder without the prosecution offering any evidence of their emotional state. The defendant's emotional state is turned into an affirmative defense.

Supreme Court Allowed New York To Make Defendants Prove Emotional State

The U.S. Supreme Court upheld a second degree murder conviction under a New York law that required the defendant to prove extreme emotional disturbance as an affirmative defense, in order to reduce his charge from murder to manslaughter. The Court ruled that a state may make a defendant prove an element of a lesser crime as an affirmative defense so long as it could convict the person of all of the elements of the crime with which it had charged him (second degree murder, in this case). The defendant appealed the murder conviction, arguing that his emotional state was an element of the crime and constitutionally could not be parceled off as an affirmative defense. The Court disagreed, holding that New York could have convicted him of murder based on its proof of the elements of second degree murder (intentional killing of a human being). The defendant's emotional state was not an element of that crime. (Patterson v. New York, 432 U.S. 197 (1977).)

The notion of what is an element of a crime and what may be treated as an affirmative defense remains in flux. State legislatures persuaded by "law-and-order" arguments have rewritten criminal laws to foist more of the burden at trial onto the criminal defendant. Civil liberties groups and public defenders argue that such machinations impose unconstitutional burdens on criminal defendants.

The Insanity Defense: A Proper Affirmative Defense, or a Way to Make the Defendant Prove a Lesser Offense?

Much of this re-tooling of criminal laws and affirmative defenses involves the insanity defense. Defendant advocates argue that a defendant's mental capacity clearly goes to his ability to form the requisite criminal intent (an element of all crimes that the prosecution must always prove), while their adversaries contend that insanity is more like an affirmative defense, because it may be invoked even if all of the other elements of a crime are proven. Some states treat mental capacity as an element of crimes to be proven by the prosecution, and others treat it as an affirmative defense to be proven by the defendant.

Affirmative Defenses Vary from State to State

The criminal codes of each state define the elements of the crimes in that state, and the elements of crimes differ from state to state. Likewise, affirmative defenses differ from state to state. And, the burden of proof for the defendant in proving an affirmative defense also differs. States are free to define elements of crimes and affirmative defenses as they see fit—unless the Supreme Court rules that they have violated the Constitution.

Little Uniformity and Constant Change

There is little uniformity across the U.S. as to what is or is not an affirmative defense and how affirmative defenses are treated at trial. This controversial area of criminal law, implicating as it does fundamental constitutional rights, continues to develop. If you have questions about affirmative defenses or other matters concerning criminal law, talk to a criminal defense lawyer in your area.

Talk to a Defense attorney
We've helped 95 clients find attorneys today.
There was a problem with the submission. Please refresh the page and try again
Full Name is required
Email is required
Please enter a valid Email
Phone Number is required
Please enter a valid Phone Number
Zip Code is required
Please add a valid Zip Code
Please enter a valid Case Description
Description is required

How It Works

  1. Briefly tell us about your case
  2. Provide your contact information
  3. Choose attorneys to contact you