The 'ne bis in idem' principle is a guarantee for the accused that he/she will not be held responsible for an act for which he/she has already been tried. This constitutes a fundamental right of the perpetrator of the punishable act, who can demand that proceedings are not commenced, or discontinued if already instituted, if criminal proceedings against him in the same case have already been validly terminated. It is generally accepted that the principle of 'ne bis in idem' chiefly serves the protection of persons judged - the sentenced and the acquitted. This principle also means that proceedings cannot be conducted with the aim of the acquittal or mitigation of penalty for someone who has been sentenced in a legally valid judgment. However, it should be noted that the 'ne bis in idem' prohibition can, in certain circumstances, be a barrier to demonstrating the innocence of the accused. Hence, it should be noted that modern criminal procedures are ruled by the principle of presumed innocence, which can only be set aside by a legally valid court decision declaring guilt of the accused. The accused is considered innocent until his/her guilt has been determined by a legally valid verdict that establishes the 'ne bis in idem' prohibition. Any natural or legal person whose legal interests have been directly infringed or threatened by a crime can count on a case examination on merits by an independent court. The right of a citizen to be heard by a court, to a just examination of his/her case by an independent and impartial court established by an act of law, is one of the fundamental human rights provided for in Art. 6 of the European Convention on Protection of Human Rights and Fundamental Freedoms.