Definition: Those which are made to punish actions committed before the existence of such laws, and which had not been declared crimes by preceding laws. Declar. of Rights, Mass. part 1, s. 24 Declar. of Rights, Maryl. art. 15. By the constitution of the United States and those of the several states, the legislatures are forbidden to pass ex post facto laws. Const. U. S. art. 1, s. 10, subd. 1.
2. There is a distinction between ex post facto laws and retrospective laws; every ex post facto law must necessarily be retrospective, but every retro-spective law is not an ex post facto law; the former only are prohibited.
3. Laws under the following circumstances are to be considered ex post facto laws, within the words and intents of the prohibition 1st. Every law that makes an act done before the passing of the law, and which was innocent when done, criminal, and punishes such action. 2d. Every law that aggravates a crime, or makes it greater than it was when committed. 3d. Every law that changes the punishment, and inflicts a greater punishment than the law annexed to the crime when committed. 4th. Every law that alters the legal rules of evidence and receives less, or different testimony, than the law required at the time of the commission of the offence, in order to convict the offender. 3 Dall. 390.
4. The policy, the reason and humanity of the prohibition against passing ex post facto laws, do not extend to civil cases, to cases that merely affect the private property of citizens. Some of the most necessary acts of legislation are, on the contrary, founded upon the principles that private rights must yield to public exigencies. 3 Dall. 400; 8 Wheat. 89; see 1 Cranch, 109; 1 Gall. Rep. 105; 9 Cranch, 374; 2 Pet. S. C. R. 627; Id. 380; Id. 523.
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