Criminal Defenses

Types of Criminal Law Defenses

In the area of criminal law, there are many ways that an accused person can escape a finding of guilt. Most commonly there are permitted ‘defenses’ that have the effect of negating the elements of a crime.

In criminal cases, the prosecuting attorney must prove that each element of a criminal offense is unlawful “beyond a reasonable doubt”. This standard is a much higher standard of proof than in a civil case, which merely seeks a “preponderance of the evidence”.

The defendant in a criminal case typically must plead any defenses and offer the relevant evidence to offer a valid defense, which then shifts the burden of proof back onto the prosecution.

This article discusses the many criminal defenses available to defendants to help mitigate the charges with a reduced punishment or avoid punishment entirely.

Elements of a Crime

The elements of any crime are defined by state law or state statute. The Model Penal Code (MPC) is a text that offers a standardized penal law and recommended punishments. The MPC is meant to provide standardized examples of criminal laws for individual states of how to define crimes. The Legislatures of each state can choose to adopt the MPC, pass their own criminal statutes, or adopt a combination of the two.

Almost every crime has three elements that a prosecutor must prove in order to prove that a defendant is guilty. The three elements of a crime are (1) the actus reus, (2) the mens rea, and (3) the concurrence of the two.

The actus reus is an overt criminal act. There has to be a physical act in furtherance of a crime in order for the actus reus element to be met. The mens rea means the mental state of the defendant at the time of the accident. It is also called “culpability.” Criminal statues identify the mental state required for to prove a particular crime. The MPC defines four mental states: purposely, knowingly, recklessly, and negligently. There are very few crimes that don’t require the defendant to act with one of these mental states. Statutory rape is the main example used for a crime that does not require purpose, knowledge, recklessness, or negligence in order for the defendant to be found guilty.

In addition to the actus reus and mens rea, the prosecutor has to prove a temporal concurrence between the two. Meaning the actus reus and mens rea need to take place at the same time.

Finally, the prosecutor must also usually show that the defendant’s conduct caused the harm. This is called actual or proximate cause. The general test for causation between the act and the harm is that the event or harm would not have happened but for the defendant’s actions.

At trial, a defendant can offer evidence of a variety of defenses to show that one of the above elements is not satisfied.

Factual Innocence

Innocence is the most powerful criminal defense, but sometimes the hardest to prove. The defendant has a constitutional right to defend himself at trial and submit any evidence that supports that he or she is factually innocent of the crime. Defendants can submit evidence in support of their innocence claim in the form of eyewitness testimony or declarations, character witnesses to attest to the defendant’s good character, phone records placing the defendant away from the scene of the crime, or even alibi witnesses.

The state has the burden to prove the defendant committed the crime beyond a reasonable doubt. The defendant does not have to prove his innocence but has to provide enough evidence to rebut the prosecution’s case.


An alibi is evidence that the defendant was not at the scene of the crime when the crime occurred. This can be proven through direct testimony from the defendant, testimony from witnesses, receipts, cell phone records, or any other reliable documents that can place the defendant somewhere else other than the scene of the crime. A defendant does not have to prove an alibi in every case in order to be found not guilty of a crime, but any evidence that the defendant did not commit the crime helps at trial.

Mental Disorder (Insanity)

A mental disorder or claim of insanity is another defense available to defendants. A defendant may argue that he cannot be found guilty for a crime because he or she did not understand that his or her actions were a crime based on a mental disorder. If a defendant proves insanity, then he will be found not guilty by reason of insanity. The insanity defense is controversial, and states generally apply four different tests to determine whether a defendant meets the definition of legally insane.

The MPC test provides that a defendant is insane when the defendant could not conform his or her actions to the requirements of the law due to a diagnosed mental disorder suffered from at the time of the crime.

Under the M’Naghten test, a defendant may be deemed insane if he or she did not understand the nature of the criminal act due to a disease of the mind. If the defendant did understand the nature of the act, then he may still be found not guilty if he did not know the act was wrong.

This rule derives from an 1843 English case where the defendant attempted to shoot England’s prime minister because he thought the Prime Minister sought to kill him. The defendant was examined by doctors, who determined he was psychotic. The defendant was found not guilty based on insanity, and England adopted the basic rule that a defendant could be found not guilty based on cognitive inability. Many states adopted the M’Naghten rule and continue to recognize an insanity defense where the defendant cannot understand right from wrong due to a mental disorder.

Proving the insanity defense requires expert testimony from medical providers that the defendant did in fact suffer from a mental disorder at the time of the criminal act.


When a defendant is intoxicated during the commission of a criminal act, he may be found not guilty. There are two intoxication defenses: voluntary intoxication and involuntary intoxication. When a defendant is voluntarily intoxicated, meaning he voluntarily ingested substances like alcohol or drugs, the defendant can use his intoxication to negate the mens rea element of the crime.

This is not a complete defense and does not apply to all types of crimes. There are generally two types of crimes, specific intent and general intent crimes. Where a defendant is charged with a specific intent crime, a jury may find that the defendant did not have the required mental state due to the intoxication. The difference between specific intent crimes and general intent crimes is confused even by courts. Specific intent crimes include, attempted crime, conspiracy, forgery, aiding and abetting and receiving stolen property, among other crimes. If a defendant is accused of a general intent crime, voluntary intoxication does not apply as a defense.

Involuntary intoxication is a complete defense, meaning the defendant cannot be found guilty if he was involuntarily intoxicated at the time of the crime. A defendant is involuntarily intoxicated where he consumed alcohol, drugs, or some other substance but did not know he was consuming the substance. Or where someone else forces or tricks a defendant into consuming an intoxicant. Because the defendant did not knowingly or voluntarily take an intoxicating substance, he or she is excused from punishment for the crime.


Automatism is a rarely used defense that refers to unconscious or involuntary conduct that is done automatically at the time of a criminal act without intent. Similar to intoxication, this defense can be used to negate the mens rea element of a crime based on the concept that a defendant cannot be held liable for actions that he is not aware of.

Mistake of Fact

A mistake of fact defense is available when a defendant misunderstands a fact that negates an element of the crime. The mistake must be both an honest mistake and one that is reasonable under the circumstances. A mistake of fact may arise in situations where a defendant is charged with larceny, but at the time the defendant took the property, the defendant reasonably believed the property was his. In order for this defense to apply, the jury or judge must find that the mistake is reasonable based on the facts present at the time of the crime.

Mistake of Law

Mistake of law is a defense where the defendant claims he or she did not know the law at the time of the crime. Generally, ignorance of the law is not an excuse to break it. However, there are limited circumstances where not knowing the law may apply. This defense applies when a law has not been published, when the defendant relied upon a law that was subsequently deemed unconstitutional, when the defendant relied upon a judicial decision that was later overturned, or when the defendant relied upon an interpretation of law by a qualified public official.

Again, a jury or judge will only find that mistake of law applies where the mistake was reasonable.

Necessity or Lesser Harm

A necessity or lesser harm defense is available when a defendant claims he or she had to commit a crime in order to prevent an even greater harm from happening.

The MPC states that necessity applies where six factors are met: (1) the presence of a clear and imminent danger, (2) the defendant reasonably believes his or her conduct will lessen the danger, (3) the defendant had no alternative to committing the criminal act, (4) the defendant did not cause or contribute to the imminent danger, (5) the defendant acted in necessity at each step, and (6) the harm caused by the defendant was lesser than the harm that was prevented.

This defense essentially requires the defendant to show he or she had to choose the lesser of two evils, which necessitated the commission of a crime.

Lawful Capacity of Office

Lawful capacity of office is a defense available to public servants. This protects people like firefighters, EMTs, and police officers from criminal liability for their action while in the line of duty. This defense exempts public servants from actions that would otherwise be a crime if normal civilians had done them. This defense is generally limited to acts one while in the course and scope of employment.

Self-Defense or Defense of Others

A defendant may claim self-defense or defense of others as a defense. In order for self-defense or defense of others to apply, the defendant’s actions must be reasonable. A defendant must reasonably believe that he or she faces imminent danger and must only use as much force as is necessary to prevent that danger. Using a gun in a fist fight, for example, may not be reasonable given the circumstances.


Duress or coercion defenses apply when a defendant commits a crime under the threat of immediate death or bodily harm. Where a defendant is forced to commit a crime against his or her own will, the defendant may be entitled to a complete defense under the theory of duress. Duress does not apply in all situations. Most states do not apply duress as a defense for murder. A defendant cannot kill someone else and be excused from liability unless the murder is in self-defense.


Consent is a defense most often used when a defendant is accused of a sexual based crime. The defendant may claim that the victim consented to the conduct. Consent must be given knowingly and voluntarily, by someone old enough and competent enough to give consent. A person who is under the age of consent, mentally incompetent, or intoxicated often cannot legally give consent. Consent may be difficult to prove where the victim claims he or she did not give consent to participate in a certain event.

Statute of Limitations or Constitutional Violations (Miranda)

Similar to civil law, most crimes have a statute of limitations. After the statute of limitations runs, the defendant cannot be charged with or found guilty of the crime—even if the defendant committed the crime. The statute of limitations is defined by state law or statute and varies depending on the crime. The purpose of statutes of limitation is to make sure that prosecutors only pursue crimes where there is reliable evidence. Memories fade over time, so the law prohibits the prosecution of a crime after a certain period.

Importantly, murder has no statute of limitations. Someone accused of murder can be arrested and charged many decades after the fact.

A defendant also has the right to a claim that his constitutional rights have been violated, which acts as sort of defense. The accused have certain due process rights under the Fifth Amendment of the Constitution. When police officers or law enforcement violate those rights, prosecution may be unconstitutional. Miranda rights, so named from the foundation Supreme Court case Miranda v. Arizona, require that police officers give certain warnings when they arrest someone for a crime.

Miranda rights include: (1) the right to remain silent, (2) warning that anything said can be used against the arrested person, (3) the right to an attorney, (4) the right to have an attorney appointed if the person arrested cannot afford one. Confessions procured without reading Miranda rights first are unconstitutional and can be challenged in court.

Constitutional protections are another layer of criminal defense where a defendant may not be punished due to violations of the law, even if the defendant committed the crime. footer logo 5