A person may escape criminal responsibility by successfully tendering a legally recognized defense to conduct that is otherwise criminal. Some defenses, such as insanity, infancy, and intoxication, are based on the defendant's lack of capacity to be held legally responsible. Other defenses such as duress, coercion, or necessity, stem from undue pressure or unusual circumstances outside of a defendant's control. An entrapment defense serves as a limitation on the powers of the government to manufacture criminal behavior.
An insane person may be unable to form the requisite intent necessary to commit a crime. Over the years a number of different approaches have been devised to determine when criminal intent is negated by insanity. The M'Naghten test is named for a delusional Englishman who believed the prime minister was trying to kill him; he mistakenly killed the prime minister's secretary instead. The psychotic M'Naghten was acquitted by an English jury in 1843 based on his insanity defense. The test requires that "at the time of the committing of the act, the party accused was labouring under such a defect of reason, from a disease of the mind, as not to know the nature and quality of the act he was doing; or if he did know it, that he did not know he was doing what was wrong."
A limited number of jurisdictions employ the irresistible impulse test to determine sanity for purposes of criminal liability. If a person's disease of mind prevents him from controlling his conduct, he may be found not guilty by reason of insanity. This defense may be used even where a person was able to distinguish between right and wrong at the time of the offense. For example, if an otherwise-sane father kills the person who molested his child, the father might claim that he was unable to control his actions because of his outrage at the molester's heinous conduct. The irresistible impulse defense fell into disfavor following John Hinckley's acquittal by reason of insanity for his 1981 attempt to assassinate President Ronald Reagan.
Also used in some jurisdictions is the Model Penal Code test of insanity (first used at large in 1960). It provides that a person is not responsible for his conduct if at the time of the conduct the he lacks the substantial capacity, because of a mental disease or defect, either to appreciate the criminality or wrongfulness of the conduct or to conform the conduct to the requirements of the law. In 1984 in response to Hinckley's acquittal, Congress passed the Insanity Defense Reform Act. The Insanity Act employs language similar to the Model Penal Code test.
Trial must be rescheduled if a defendant is insane at the time of trial. The Supreme Court has ruled that a defendant must have the present ability to consult with a lawyer with a reasonable degree of rational understanding, and must have a rational and a factual understanding of the proceeding against him. A convict who goes insane after imposition of a death sentence is entitled to a stay of execution until adjudged sane.
Infancy is a lack of legal capacity to be held responsible for a crime due to the age of the perpetrator. At common law, a child under the age of seven was presumed incapable of committing a crime. Between ages seven and 14, a rebuttable presumption existed that a juvenile was incapable of committing a crime. This presumption weakened progressively as the child approached age 14. Presently, most states define juveniles as persons under the age of 18, although a some states denominate 17 or 16. Juvenile cases are handled under a different system than adult criminal cases. After a certain age, typically set between 13 and 15, a juvenile who commits a serious crime may have his case transferred to adult court and tried as an adult.
Voluntary intoxication caused by drugs or alcohol is permitted as a defense only in very rare instances. It may be allowed as a defense in some situations where specific intent is required; the intoxication may negate the requisite mental state required to establish the offense. Involuntary intoxication, where a defendant is forced to take intoxicants or imbibes without knowledge or reason to know of the intoxicating character, is treated much like an insanity defense.
Duress and coercion are defenses seldom used. These ask the court to treat an alleged perpetrator as a victim, as when a bank robber says he had to do it or his partner would have killed him. A successful defense usually requires a threat of death or serious bodily harm to oneself (or sometimes to a close relative); most states do not recognize duress or coercion to excuse murder charges. Patricia Hearst unsuccessfully invoked this defense in a widely-followed case during the 1970s. Hearst, daughter of wealthy newspaper owners, was kidnapped by social revolutionaries, then later participated with her captors in an armed bank robbery.
Necessity differs from coercion in that it provides an excuse from criminal liability where, in order to protect life or limb, a person reasonably has no other acceptable choice than to commit a criminal act. For example, a defendant who is fleeing a gun-toting criminal may invoke a defense of necessity if when fleeing, the defendant had to break and enter into the dwelling of another.
Entrapment is a defense developed to prevent government officials from inducing a person to commit a crime, where that person was not previously disposed to commit the crime. Entrapment as a defense does not rule out some deception on the part of the police. A person who was planning or willing to commit a crime may generally not invoke an entrapment defense where officials merely create an opportunity for commission of the crime.
- Criminal Law - Inchoate Or Prepatory Crimes: Attempt, Conspiracy, And Aiding And Abetting
- Criminal Law - Elements Of A Crime: Mens Rea And Actus Reus
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