To convict a criminal defendant, the prosecutor must prove guilt beyond a reasonable doubt. Of course, the defendant gets an opportunity to present a defense. There are many defenses, from "I didn't do it" to "I did it, but it was self-defense” and beyond. Read more about some common defenses below.
(For much more on the available defenses in criminal cases, see our topic page on Defenses to Criminal Charges.)
Didn't Do It
Most often, defendants go with the claim that they simply did not commit the alleged act in question.
The Presumption of Innocence
All people accused of crime are legally presumed to be innocent until the point of conviction, whether that comes by way of trial or plea. This presumption means that the prosecution must convince the jury of the defendant's guilt, rather than the defendant having to prove innocence. A defendant may simply remain silent and not present any witnesses, then argue that the prosecution failed to prove its case. But, in practice, defense attorneys often present their own witnesses in order to counteract the government’s case.
The prosecutor must convince the fact-finder of the defendant’s guilt "beyond a reasonable doubt." This heavy burden of proof requires that the jury (in some cases, the judge) have a moral certainty that the defendant is guilty. With such a high burden on the opposition, defense attorneys often impress upon juries that thinking the defendant committed the crime isn’t enough for a conviction.
The Alibi Defense
An alibi defense consists of evidence that the defendant was somewhere other than the scene of the crime at the time of the crime. For example, assume that Jones is accused of committing a burglary on Hampton Street at midnight on September 14. Alibi evidence might consist of a friend’s testimony that he and Jones were at the movie theatre from 11:00 p.m. to 1:00 a.m. on the night of the 14th. Additional alibi evidence would be the movie tickets and a credit card statement showing that Jones purchased them shortly before 11:00 p.m.
The Defendant Did It, But...
Sometimes an acquittal is the result even if the prosecutor showed that that the defendant did, without a doubt, commit the alleged act. (For more on this issue, see Jury Behavior.)
Self-defense is commonly asserted by those charged with crimes of violence, such as battery, assault with a deadly weapon, or murder. The defendant admits that he or she did in fact use violence, but claims that it was justified by the other person's threatening or violent actions. The core issues in self-defense cases often are:
- Who was the aggressor?
- Was the defendant's belief that self-defense was necessary a reasonable one?
- If so, was the amount force the defendant used also reasonable?
Self-defense is rooted in the belief that people should be allowed to protect themselves. In part, this means that someone doesn’t necessarily have to wait to the point of actually being struck in order to act in self-defense. Whatever the circumstances are, any force that the would-be defendant uses has to be reasonable under the circumstances. (For a more complete picture of this defense, see Self-Defense.)
The Insanity Defense
The insanity defense is generally based on the principle that punishment is justified only where defendants are capable of controlling their behavior and understanding that what they’ve done is wrong. The insanity defense prevents some people who can't function fully from being criminally punished. (For much more on insanity, including the procedures and different tests for determining it, see Pleading Insanity in a Criminal Case.)
The insanity defense is an extremely complex topic; many scholarly works are devoted entirely to explaining its nuances. Here are some major points of interest:
- Despite popular perceptions to the contrary, defendants rarely enter pleas of "not guilty by reason of insanity." When they do, they often have a hard time proving it. (Insanity is just one exception to the general rule that the prosecution must prove all components of a case beyond a reasonable doubt and that the defendant need prove nothing.)
- Various definitions of insanity are in use because neither the legal system nor mental health professionals can agree on a single meaning of the concept in the criminal law context. Among the most popular definitions is the "M’Naghten rule," which essentially defines insanity as the inability to distinguish right from wrong. Another common test is known as "irresistible impulse," which applies to someone who may know that an act is wrong, but because of mental illness be unable to resist committing it.
- Defendants found not guilty by reason of insanity are not automatically set free. They are usually confined to mental institutions. These defendants can spend more time in a mental institution than they would have spent in prison had they been convicted.
- An insanity defense normally rests largely on psychiatrists or psychologists, who testify after examining the defendant, his or her history, and the facts of the case. Courts appoint mental health professionals at government expense to assist poor defendants who cannot afford to hire their own.
Under the Influence
Defendants who commit crimes under the influence of drugs or alcohol sometimes argue that their mental functioning was so impaired that they cannot be held accountable for their actions. Generally, however, voluntary intoxication does not excuse criminal conduct. The theory is that defendants know (or should know) how alcohol and drugs affect functioning, and that they shouldn’t be off the hook because they chose to get themselves intoxicated. (For much more on the law, see Being Drunk: A Defense to Criminal Charges?)
Some states have an exception to this general rule: If the defendant is accused of committing a crime that requires "specific intent," he can argue that he was too drunk or high to have formed that intent. (Specific intent generally describes a situation where the defendant intends the precise consequences of an act in addition to intending the act itself—see General Intent Crimes vs. Specific Intent Crimes.) Specific intent may be only a partial defense, however. For example, it might lead to an acquittal for assault with specific intent to kill but a conviction of assault with a deadly weapon, the latter of which typically doesn't require specific intent.
Entrapment occurs when the government induces a person to commit a crime that he wouldn’t have otherwise committed. However, law enforcement officers can provide opportunities for defendants to commit crimes without committing entrapment. Entrapment is often a difficult to prove. (For a detailed discussion of it, see Entrapment as a Defense to a Criminal Charge.)
If you face criminal charges, consult an experienced criminal defense attorney. A knowledgeable lawyer will be able to fully explain the applicable law and protect your rights. For help finding a lawyer in your area, check out Nolo's trusted Lawyer Directory.