The variant nullum crimen sine lege ("no crime without law") establishes that conduct is not criminal if not found among the behavior/circumstance combinations of a statute.
[1] Despite the use of Latin language and brocard-like[2] appearance, the formula was mostly born in 18th century liberalism (some elements of non-retroactivity of laws and limiting the punishment to the one prescribed in the statute date back to Roman times).
In relation to the Ezekiel-commentary of Jerome,[9] Thomas Aquinas and Francisco Suárez analysed the formal conditions of the punishment of conscience.
According Suárez the punishment of conscience is the insight in an obligation to act in concordance with the human nature to undo a past misdeed.
[17] When coming to terms with the Nazi crimes after World War II in Austria, the Austrian legal scholar and judge Wilhelm Malaniuk justified the admissibility of the non-application of the "nulla poena sine lege" with regard to the Austrian Verbotsgesetz 1947: "Because these are crimes that are so grossly violate the laws of humanity!"
[22] Thus, prosecutions have been possible of such individuals as Nazi war criminals[23] and officials of the German Democratic Republic responsible for the Berlin Wall,[24] even though their deeds may have been allowed or even ordered by domestic law.
because generally, in the legal systems of mainland Europe where the maxim was first developed, "penal law" was taken to mean statutory penal law, so as to create a guarantee to the individual, considered as a fundamental right, that he would not be prosecuted for an action or omission that was not considered a crime according to the statutes passed by the legislators in force at the time of the action or omission, and that only those penalties that were in place when the infringement took place would be applied.
point out that a prohibition in a general principle does not amount to the establishment of a crime, and that the rules of international law also do not stipulate specific penalties for the violations.
In an attempt to address those criticisms, the statute of the recently established International Criminal Court provides for a system in which crimes and penalties are expressly set out in written law, that shall only be applied to future cases.
[25] The principle of nulla poena sine lege, insofar as it applies to general criminal law, is enshrined in several national constitutions, and international instruments, see European Convention on Human Rights, article 7(1).