Ex post facto
An Ex post facto law, translated as "after the fact," is defined as one which: (a) makes criminal an act done before the passage of the law and which was innocent when done, and punishes such an act; (b) aggravates a crime, or makes it greater than it was, when committed; (c) changes the punishment and inflicts a greater punishment than the law annexed to the crime when committed; (d) alters the legal rules of evidence, and authorizes conviction upon less or different testimony than the law requires at the time of the commission of an offense in order to convict the defendant. ; (e) assumes to regulate civil rights and remedies only, in effect imposes penalty or deprivation of a right for something which when done was lawful, and; (f) deprives a person accused of a crime of some lawful protection to which he has become entitled, such as the protection of a former conviction or acquittal, or a proclamation of amnesty . 
The Bill of Rights of the Constitution of the Philippines states that "Sec. 22: No ex post facto law or bill of attainder shall be enacted." Applying this constitutional provision, the Supreme Court of the Philippines has held that the prohibition applies only to criminal legislation which affects the substantial rights of the accused. It also applies to criminal procedural law prejudicial to those persons accused of a crime.
The prohibition against the passage of an ex post facto law, expressed in the legal maxim "nullum crimen, nulla poena sine lege (there is no crime, where there is no law punishing it), is embodied in Art. 21 of the Revised Penal Code which states that: "[n]o felony shall be punishable by any penalty not prescribed by law prior to its commission."
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