http://en.wikipedia.org/wiki/Miscarriage_of_justice
A miscarriage of justice is primarily the conviction and punishment of a person for a crime that he or she did not commit. The term can also be applied to errors in the other direction — "errors of impunity" — and to civil cases, but those usages are rarer, though the occurrences appear to be much more common. Most criminal justice systems have some means to overturn, or "quash", a wrongful conviction, but this is often difficult to achieve. The most serious instances occur when a wrongful conviction is not overturned for several years, or until after the innocent person has been executed or died in jail.
