laws ex post fact

LAWS EX POST FACTO. 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 
retrospective 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.