A person charged with a crime will be presumed innocent, and the onus is on the prosecutor to prove the defendant’s guilt beyond a reasonable doubt. There are a wide range of defenses that the defendant may opt to invoke; however, some defenses are selected more regularly than others.

1. It Wasn’t Me

Probably the most popular defense of a criminal defendant, even a person with strong evidence against them, is a denial of any involvement whatsoever. “It wasn’t me,” “I didn’t do it” or “I wasn’t even there” are frequent responses when accused of criminal action. Having a good alibi will strengthen the defendant’s fight against the charge, as the burden of proof lies entirely on the prosecution.

In cases where there is little or no evidence, the defendant may be successful, yet some defendants may still be found guilty based on circumstantial evidence. History is littered with cases of individuals being incarcerated for years when they were not the perpetrators of the crimes.

2. Mistake of Fact

A defendant may claim that the crime they are charged with committing arose out of a mistake of fact. A mistake of fact can insulate the defendant against the mens rea element needed to secure a conviction on the charge. In order to avoid liability, the defendant must show that they held an honest and reasonable belief that their action was legal, based on a misunderstanding of the facts.

A mistake of fact differs from a mistake of law, which is rarely seen as an acceptable defense.

3. Insanity or Mental Disorder

If a crime was committed as a result of a mental disorder, the defendant may plead the insanity defense. A court will wish to see one or more psychiatrists’ reports following a clinical examination of the defendant to determine whether a mental disorder was the reason for the defendant’s behavior. As a means of avoiding incarceration, it is a risky plea where the defendant is just pretending to be insane.

The usual result of an insanity plea is confinement to a mental institution for treatment and supervision. There is always the possibility that the term of confinement will exceed the term of a prison sentence.

4. Intoxication

A defendant suffering from intoxication at the time of the crime may claim that their mental functions were impaired. This plea is useful if the crime was one that required a "specific intent" on the defendant’s part. Specific intent requires that the defendant intentionally committed the act knowing what the outcome would be.

The defendant will need to show that they were too drunk to have formed the necessary intent. Voluntarily getting drunk and then committing a criminal act will rarely excuse a defendant from criminal liability, but may help with mitigation.

5. Duress

A defendant who was forced by another person to carry out an action against their will may seek to rely on duress as a defense. In order to succeed as a defense, there must be a serious threat of danger or bodily injury to the defendant, and the threat must be a continuous and present one. The defendant’s fear must be also reasonable. A person with a gun pointed at them, for example, would reasonably feel considerable fear.

Usually, neither a past threat nor a threat of harm in the future will suffice. The defense will also fail if the defendant could have avoided the immediate danger by ways other than committing a crime. Additionally, if the defendant acted negligently or recklessly in placing themselves at risk of danger from the outset, their actions will be held against them. In many states, the defense of duress is unavailable for certain crimes like murder.

6. Necessity

The defense of necessity is somewhat similar to that of duress in that the defendant must feel compelled to act in an unlawful manner to thwart immediate danger. The justification for their action is that the situation was one of overwhelming urgency, requiring the defendant to prevent harm from occurring. To be successful as a defense, the individual must show that:

  • their behavior did not contribute to or cause the threat to arise;
  • they held a reasonable belief that there was no other realistic alternative action to be taken under the circumstances other than committing the crime; and
  • the action taken to dispel the threat did not result in greater harm than would have occurred had the defendant taken no action.

For example, an individual who breaks and enters private property in order to put out a fire may seek to rely on the defense of necessity.

7. Self-Defense

A person under attack has a right to defend themselves and does not have to wait to be attacked before reacting to the threat. The defense of self-defense may succeed where there is no doubt that the defendant committed the act of which they are accused. Usually, the type of crime involves some form of violence, such as battery or assault, or even murder. The main questions that the court will consider in determining whether the defendant’s actions were justified are:

  • Which party was the aggressor?
  • Was the defendant’s response a reasonable one?
  • Was the amount of force used to repel the violence reasonable?

8. Entrapment

The defense of entrapment is usually raised in criminal cases involving law enforcement or other government agents, and their interaction with defendants prior to the commission of a crime.

Law enforcement officers are allowed to carry out sting operations, for example, leaving "bait packages" on porches in an effort to catch package thieves. However, officers are not allowed to encourage a person to steal a package by telling them where the item is located and how to steal it. If the defendant would not have stolen the package but for the officers coercing them to do so, their actions may constitute entrapment.

In some states, an objective approach is taken as to whether the defendant was entrapped. Under the objective approach, jurors will decide whether the officer’s actions induced the defendant to commit the crime. In other states, there is a subjective approach in which the jury decides whether the defendant’s predisposition to commit the crime was what caused them to act and not what the officer said or did.