The jury trials
If you are interested, the jury trials were invented in the Dark Ages in Britain shortly after the Anglo-Saxon invasion. Some sources point to Greece, but their system was different. In Greece, the whole attending audience decide first the guilt then the punishment. The 12 jurors in Britain were originally self-informed (from the local nobles); the first account of such a jury is from the Wantage Code of Ethelred. Each juror individually investigated (sic!) the case; the fate was decided by ordeal:

...the aristocratic jury of presentment...initiated the prosecution of suspected persons in the court of the wapentake. ...the twelve leading thegns in each wapentake were to go out from the court and swear that they would neither accuse the innocent nor protect the guilty. Thus the sworn jury, hitherto unknown to English law, came into being in a most important document in English legal history. The fate of the suspect, however, was still settled by ordeal, not by the judgment of the thegns who presented them. http://www.britannia.com/history/narsaxhist2.html

The jury as we know it was introduced by Henry II in 1166 to replace the Norman custom of the trial by ordeal. How the jury trials have originated in the Anglo-Saxon past and why Henry II decided to revive the jury institution is not known. Perhaps most people living today would agree that the trial by jury is better than the trial by ordeal. The system worked so well that no other change was needed in 840 years. The purpose of the jury is to deliver justice. The world justice in English originates from c. 1200. In the English-speaking world, the notion of "justice" includes the trial by jury. The alternatives are possible, but what is delivered there is not justice.