Nullum crimen, nulla poena sine lege (Latin: "no crime, no punishment without law") is the principle of legality in criminal law. A person may be convicted only for conduct that was defined as a criminal offence by a law in force at the time it was committed, and may receive only a penalty that the law then provided.
Components
The principle is usually understood to require that criminal law be written (lex scripta), so that crimes are created by statute rather than custom or judicial invention; prior (lex praevia), so that it does not apply retroactively; certain (lex certa), so that offences are defined clearly enough for people to know what is forbidden; and strict (lex stricta), so that it is not extended by analogy to the detriment of the accused.
Sources
The principle was formulated by the German jurist Paul Johann Anselm von Feuerbach in the early nineteenth century and is now protected by Article 11(2) of the Universal Declaration of Human Rights and Article 15 of the International Covenant on Civil and Political Rights.
In Indonesia
Article 1 of the Indonesian Criminal Code embodies the principle of legality, and Article 28I(1) of the 1945 Constitution lists the right not to be prosecuted on the basis of retroactive law among the rights that cannot be limited under any circumstances. Where the law changes after an act is committed, the provision most favourable to the defendant applies.
Exceptions Debated
International criminal law permits prosecution of acts that were criminal according to the general principles of law recognised by the community of nations, which has allowed trials for genocide and crimes against humanity.