Jury nullification (US/UK), jury equity (UK), or a perverse verdict (UK) occurs when the jury in a criminal trial gives a not guilty verdict regardless of whether they believe a defendant has broken the law. The jury's reasons may include the belief that the law itself is unjust, that the prosecutor has misapplied the law in the defendant's case, that the punishment for breaking the law is too harsh, or general frustrations with the criminal justice system. Some juries have also refused to convict due to their own prejudices in favor of the defendant. Such verdicts are possible because a jury has an absolute right to return any verdict it chooses.
Nullification is not an official part of criminal procedure, but is the logical consequence of two rules governing the systems in which it exists: Jurors cannot be punished for passing an incorrect verdict. In many jurisdictions, a defendant who is acquitted cannot be tried a second time for the same offence.
A jury verdict that is contrary to the letter of the law pertains only to the particular case before it. However, if a pattern of acquittals develops in response to repeated attempts to prosecute a particular offence, this can have the de facto effect of invalidating the law. Such a pattern may indicate public opposition to an unwanted legislative enactment. It may also happen that a jury convicts a defendant even if no law was broken, although such a conviction may be overturned on appeal. Nullification can also occur in civil trials, but (unlike in criminal trials) if the jury renders a not liable verdict that is clearly at odds with the evidence, the judge can issue a judgment notwithstanding the verdict, or order a new trial.
Background
In the past, it was feared that a single judge or panel of government officials might be unduly influenced to follow established legal practice, even when that practice had drifted from its origins. In most modern Western legal systems, judges often instruct juries to act only as "finders of fact", whose role it is to determine the veracity of the evidence presented, the weight accorded to the evidence, to apply that evidence to the law as explained by the judge, and to reach a verdict; but not to question the law itself. Similarly, juries are routinely cautioned by courts and some attorneys not to allow sympathy for a party or other affected persons to compromise the fair and dispassionate evaluation of evidence. These instructions are criticized by advocates of jury nullification. Some commonly cited historical examples of jury nullification involve jurors refusing to convict persons accused of violating the Fugitive Slave Act by assisting runaway slaves or being fugitive slaves themselves, and refusal of American colonial juries to convict a defendant under English law.
Jury nullification is the source of much debate. Some maintain that it is an important safeguard of last resort against wrongful imprisonment and government tyranny. Some view it as a violation of the right to a jury trial, which undermines the law; whereas others, such as those members of Congress who voted to impeach Supreme Court Justice Samuel Chase for instructing a jury against nullification, view a jury as a body charged with judging both law and fact. Some view it as a violation of the oath sworn by jurors. In the United States, some view the requirement that jurors take an oath to be unlawful in itself, while still others view the oath's reference to "deliverance" to require nullification of unjust law: "will well and truly try and a true deliverance make between the United States and the defendant at the bar, and a true verdict render according to the evidence, so help [me] God".
Some fear that nullification could be used to permit violence against socially unpopular factions. They point to the danger that a jury may choose to convict a defendant who has not broken the letter of the law. However, judges retain the rights both to decide sentences and to disregard juries' guilty verdicts, acting as a check against malicious juries. Jury nullification may also occur in civil suits, in which the verdict is generally a finding of liability or lack of liability (rather than a finding of guilty or not guilty).
The main ethical issue involved in jury nullification is the tension between democratic self-government and integrity. The argument has been raised that prosecutors are not allowed to seek jury nullification, and therefore defendants should not be allowed to seek it either. However, for a prosecutor to nullify a law in this context would require negating the presumption of innocence. (For this reason, prosecutorial nullification is typically defined as declining to prosecute.)