A miscarriage of justice primarily is the conviction and punishment of a person for a crime he or she did not commit. The term can also apply to errors in the other direction—"errors of impunity", and to civil cases. Most criminal justice systems have some means to overturn, or "quash", a wrongful conviction, but this is often difficult to achieve. In some instances a wrongful conviction is not overturned for several years, or until after the innocent person has been executed, released from custody, or has died.
"Miscarriage of justice" is sometimes synonymous with wrongful conviction, referring to a conviction reached in an unfair or disputedtrial. Wrongful convictions are frequently cited by death penalty opponents as cause to eliminate death penalties to avoid executing innocent persons. In recent years, DNA evidence has been used to clear many people falsely convicted.
While a miscarriage of justice is a Type I error for falsely identifying culpability, an error of impunity would be a Type II error of failing to find a culpable person guilty. However, the term "miscarriage of justice" is often used to describe the latter type as well.
The Scandinavian languages (viz. Danish, Norwegian and Swedish) have a word, the Swedish variant of which is justitiemord, which literally translates as "justice murder." The term exists in several languages and was originally used for cases where the accused was convicted, executed, and later cleared after death. With capital punishment decreasing, the expression has acquired an extended meaning, namely any conviction for a crime not committed by the convicted. The retention of the term "murder" represents both universal abhorrence against wrongful convictions and awareness of how destructive wrongful convictions are. Some Slavic languages have also the word (justičná vražda in Slovak, justiční vražda in Czech) which literally translates as "justice murder", but it is used for Judicial murder, while miscarriage of justice is "justiční omyl" in Czech, implying an error of the justice system, not a deliberate manipulation.
Also, the term travesty of justice is sometimes used for a gross, deliberate miscarriage of justice. The usage of the term in a specific case is, however, inherently biased due to different opinions about the case. Show trials (not in the sense of high publicity, but in the sense of lack of regard to the actual legal procedure and fairness), due to their character, often lead to such travesties.
The concept of miscarriage of justice has important implications for standard of review, in that an appellate court will often only exercise its discretion to correct plain error when a miscarriage of justice (or "manifest injustice") would otherwise occur.
Causes of miscarriages of justice include:
- Plea bargains that offer incentives for the innocent to plead guilty, sometimes called an innocent prisoner's dilemma
- Confirmation bias on the part of investigators
- Withholding or destruction of evidence by police or prosecution
- Fabrication of evidence or outright perjury by police (see testilying), or prosecution witnesses (e.g., Charles Randal Smith)
- Biased editing of evidence
- Prejudice against the class of people to which the defendant belongs
- Misidentification of the perpetrator by witnesses and/or victims
- Overestimation/underestimation of the evidential value of expert testimony
- Contaminated Evidence
- Faulty forensic tests
- False confessions due to police pressure or psychological weakness
- Misdirection of a jury by a judge during trial
- Perjured evidence by the real guilty party or their accomplices (frameup)
- Perjured evidence by supposed victim or their accomplices
- Conspiracy between court of appeal judges and prosecutors to uphold conviction of innocent
Risk of miscarriages of justice is one of the main arguments against the death penalty. Where condemned persons are executed promptly after conviction, the most significant effect of a miscarriage of justice is irreversible. Wrongly executed people nevertheless occasionally receive posthumous pardons—which essentially void the conviction—or have their convictions quashed. Many death penalty states hold condemned persons for ten or more years before execution, so that any new evidence that might acquit them (or, at least, provide reasonable doubt) will have had time to surface.
Even when a wrongly convicted person is not executed, years in prison can have a substantial, irreversible effect on the person and their family. The risk of miscarriage of justice is therefore also an argument against long sentences, like life sentence, and cruel sentence conditions.