Ne bis in idem, which translates literally from Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 as "not twice in the same", means that no legal action can be instituted twice for the same cause of action. It is a legal concept originating in Roman Civil Law

Roman law

Roman law is the legal system of ancient Rome, and the legal developments which occurred before the 7th century AD — when the Roman–Byzantine state adopted Greek as the language of government. The development of Roman law comprises more than a thousand years of jurisprudence — from the Twelve...

, but it is essentially the double jeopardy

Double jeopardy

Double jeopardy is a procedural defense that forbids a defendant from being tried again on the same, or similar charges following a legitimate acquittal or conviction...

(autrefois acquit) clause found in common law

Common law

Common law is law developed by judges through decisions of courts and similar tribunals rather than through legislative statutes or executive branch action...

 jurisdictions.

The International Covenant on Civil and Political Rights

International Covenant on Civil and Political Rights

The International Covenant on Civil and Political Rights is a multilateral treaty adopted by the United Nations General Assembly on December 16, 1966, and in force from March 23, 1976...

 guarantees the right to be free from double jeopardy; however, it does not apply to prosecutions by two different sovereigns (unless the relevant extradition treaty expresses a prohibition). The Rome Statute of the International Criminal Court

Rome Statute of the International Criminal Court

The Rome Statute of the International Criminal Court is the treaty that established the International Criminal Court . It was adopted at a diplomatic conference in Rome on 17 July 1998 and it entered into force on 1 July 2002. As of 13 October 2011, 119 states are party to the statute...

 creates a different form of ne bis in idem.

Rome Statute and ad hoc UN tribunals

The Rome Statute establishing the International Criminal Court (ICC) states that the ne bis in idem principle has a peculiar meaning, especially if compared to European supranational law. The ICC jurisdiction is complementary to national law, and article 20 of the Rome Statute clearly specifies that, even if the principle shall subsist in general terms, this cannot be taken in consideration in case one of the two conditions (unwillingness and incapability) of existence of the supranational court's jurisdiction occurs.
Article 10 of ICTY Statute and article 9 of ICTR

International Criminal Tribunal for Rwanda

The International Criminal Tribunal for Rwanda is an international court established in November 1994 by the United Nations Security Council in Resolution 955 in order to judge people responsible for the Rwandan Genocide and other serious violations of international law in Rwanda, or by Rwandan...

Statute state that the non bis in idem principle can be enforced mainly to clarify that the ad hoc tribunal's sentences are "stronger" than the ones in domestic courts. In other words, national courts cannot proceed against the responsible parties of crimes falling in the tribunal's jurisdiction if the international tribunal has already pronounced sentence for the same crimes. However, ICTY and ICTR can judge alleged criminals already sentenced by national courts if:

• the sentence defined the crimes as "ordinary", and
• the judiciary of the state is not considered impartial, the domestic trial is considered a pretence to protect the accused from the legal action of international justice, or the domestic trial is considered as not fair on some fundamental legal basis.