Finally, regulations need to apply non-retroactively or not retroactively. This means that a person cannot be punished for his actions in the past based on regulations that exist in the future. This nature needs to be fulfilled because retroactive regulations violate one of human rights.

To answer the second question, legal experts agree that no act can be punished by future regulations. This is related to the previous discussion regarding the non-retroactive nature of regulations. However, in practice, this idea occurs.

One form of criminal regulation that applies the principle of retroactivity is Law Number 15 of 2003 concerning the Stipulation of Government Regulations in Lieu of Law Number 1 of 2002 concerning the Eradication of Terrorism Crimes ("UU 15/2003"). This regulation punishes acts of terrorism after many cases of terrorism occurred in Indonesia. For example, this regulation was used to indict Amrozi Cs. who was the mastermind of the Bali Bomb I case in 2002.

Implementation of the Legality Principle

The principle of legality was born from the thinking of von Feuerbach, a legal scholar in Germany who lived from 1775 to 1833. Feuerbach initiated this principle by referring to the practice in ancient Roman times which punished every act criminal extra ordinaria.

Criminal extra ordinaria is a term for any act that the ruler considers a crime. Criminal extra ordinaria is not regulated by law, but depends entirely on the interpretation of the ruler. Consequently, the ruler can be arbitrary in subjectively determining a form of act as a crime.

The authoritarian attitude of the ruler in determining criminal extra ordinaria eventually sparked a movement against the ruler's absolutism. At this point, the idea of the principle of legality emerged. This principle became a guideline for the formation of regulations that impose criminal sanctions on perpetrators of crimes.

Feuerbach connects the principle of legality with the theory of vom psychologischen zwang. Integratively, he advocated that, in determining prohibited acts in regulations, there must be regulations regarding the type of act and the type of crime that can be imposed. That way, people who are going to commit prohibited acts will first know the legal consequences they will face before they commit a crime.

Feuerbach also asserted that this principle is not only related to legal certainty, but also to legal justice. Therefore, he emphasized that everyone must be presumed innocent until proven otherwise, and the court must guarantee the protection of individual rights listed in law.

Feuerbach's ideas can be found in several thoughts of French revolutionaries, such as Montesquieu in his book L'esprit des Lois (1748) and Rousseau in his book Dus Contract Social (1762). During the French government by Napoleoon Bonaparte, the principle of legality was included in Article 4 Code Penal and then adopted by the Netherlands through Wetboek v. Strafrecht Nederland 1881.

Due to the principle of concordance during the Dutch colonial period, Indonesia also used the principle of legality adopted through the Criminal Code. The existence of the principle of legality guarantees that the implementation process criminal law in Indonesia guarantees respect for individual rights, while preventing the intervention of authoritarian rulers that could endanger the lives of Indonesian citizens.