When a jury lets guilty people go free, it is called jury nullification. When a prosecutor decides not to charge a guilty person of a crime, it is called "prosecutorial discretion". Prosecutors are legal professionals while jury members are not. However prosecutors are also politicians and may make politically motivated decisions or may be corrupt. Judges will often instruct a jury to return a verdict based on the merits of the case and not the merits of the law. But one argument is that juries have a responsibility to decide if they think the law is wrong in a particular case. 