An ex post facto law (from the Latin for "after the fact") or retroactive law, is a law that retroactively changes the legal consequences of acts committed or the legal status of facts and relationships that existed prior to the enactment of the law. In reference to criminal law, it may criminalize actions that were legal when committed; or it may aggravate a crime by bringing it into a more severe category than it was in at the time it was committed; or it may change or increase the punishment prescribed for a crime, such as by adding new penalties or extending terms; or it may alter the rules of evidence in order to make conviction for a crime more likely than it would have been at the time of the action for which a defendant is prosecuted. Conversely, a form of ex post facto law commonly known as an amnesty law may decriminalize certain acts or alleviate possible punishments (for example by replacing the death sentence with life-long imprisonment) retroactively.
A law may have an ex post facto effect without being technically ex post facto. For example, when a law repeals a previous law, the repealed legislation no longer applies to the situations it once did, even if such situations arose before the law was repealed. The principle of prohibiting the continued application of these kinds of laws is also known as Nullum crimen, nulla poena sine praevia lege poenali.
Generally speaking, ex post facto penal laws are seen as a violation of the rule of law as it applies in a free and democratic society. Most common law jurisdictions do not permit retroactive criminal legislation, though some have suggested that judge-made law is retroactive as a new precedent applies to events that occurred prior to the judicial decision. In some nations that follow the Westminster system of government, such as the United Kingdom, ex post facto laws are technically possible as the doctrine of parliamentary supremacy allows parliament to pass any law it wishes. However, in a nation with an entrenched bill of rights or a written constitution, ex post facto legislation may be prohibited.
Ex post facto is the uncomplimentary characterization of law and legislation that applies retroactively (i.e. "from a thing done afterward").
Retroactive laws designed to prosecute what was perceived to have been a blatantly unethical means of tax avoidance were passed in the early 1980s by the Fraser government (see Bottom of the harbour tax avoidance).
According to the 5th Article, XXXVI of Brazilian Constitution, ex post facto laws are prohibited in subject of acquired rights, perfect juridicly acts and res judicata. Like France, there is an exception, when retroactive criminal laws benefits the accused person. and or doomed
Some scholars assert that the Nuremberg Trials following World War II were based on ex post facto law, because the Allies did not negotiate the London Charter, defining crimes against humanity and creating the International Military Tribunal, until well after the acts charged. Others, including the International Military Tribunal, argued that the London Charter merely restated and provided jurisdiction to prosecute offenses that were already made unlawful by the Kellogg-Briand Pact, the Covenant of the League of Nations, and the various Hague Conventions.
In India without using the expression "Ex post facto law" the underlying principle has been adopted in the Article 20 (1) of the Indian Constitution in the following words:
"No person shall be convicted of any offence except for violation of a law in force at the time of the commission of the act charged as an offence, nor be subjected to a penalty greater than that which have been inflicted under the law in force at the time of commission of the offence."
Ex post facto criminal laws are prohibited by Article 7 of the European Convention on Human Rights, to which the United Kingdom is a signatory, but parliamentary sovereignty, in theory, takes priority even over this.
However, not all laws with ex post facto effects have been found to be unconstitutional. One current U.S. law that has an ex post facto effect is the Adam Walsh Child Protection and Safety Act of 2006. This law, which imposes new registration requirements on convicted sex offenders, gives the U.S. Attorney General the authority to apply the law retroactively. The U.S. Supreme Court ruled in Smith v. Doe (2003) that forcing sex offenders to register their whereabouts at regular intervals and the posting of personal information about them on the Internet does not violate the constitutional prohibition against ex post facto laws, because compulsory registration of offenders who completed their sentences before new laws requiring compliance went into effect does not constitute a punishment.
Another example is the so-called Lautenberg law where firearms prohibitions were imposed on those convicted of misdemeanor domestic violence offenses and subjects of restraining orders (which do not require a criminal conviction). These individuals can now be sentenced to up to 10 years in a federal prison for possession of a firearm, regardless of whether or not the weapon was legally possessed at the time the law was passed. Among those that it is claimed the law has affected is a father who was convicted of a misdemeanor of child abuse despite claims that he had only spanked his child, since anyone convicted of child abuse now faces a lifetime firearms prohibition. The law has been legally upheld because it is considered regulatory, not punitive - it is a status offense.
Finally, Calder v. Bull expressly stated that a law that "mollifies" a criminal act was merely retrospective and not an ex post facto law.
A large "exception" to the ex post facto prohibition can be found in administrative law, as federal agencies may apply their rules retroactively if Congress has authorized them to do so. Retroactive application is disfavored by the courts for a number of reasons, but Congress may grant agencies this authority through express statutory provision. Furthermore, when an agency engages in adjudication, it may apply its own policy goals and interpretation of statutes retroactively, even if it has not formally promulgated a rule on a subject.
Therefore, ex post facto or ex postfacto is natively an adverbial phrase, a usage demonstrated by the sentence "He was convicted ex post facto (i.e., from a law passed after his crime)." The law itself would rightfully be a postfactum law (lex postfacta); nevertheless, despite its redundant or circular nature, the phrase an ex post facto law is used.
In Poland the phrase lex retro non agit ("the law does not operate retroactively") is often used.
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Criminal Law - Fourth Circuit Holds Retroactive Application of Federal Sentencing Guidelines Amendments Violates Ex Post Facto Clause
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