Ex Post Facto Clause California Constitution
The United States Constitution (art. I, 9 & 10) and the California Constitution (art. I, 9) prohibit the passage of ex post facto laws.
The interpretation of the ex post facto clauses in the United States and California Constitutions is identical. (People v. McVickers (1992) 4 Cal. 4th 81, 84, 840 P.2d 955.)
Under Collins v. Youngblood (1990) 497 U.S. 37, 42, 111 L. Ed. 2d 30, 110 S. Ct. 2715, (Collins) the high court interpreted the ex post facto clause to prohibit legislation:
" which punishes as a crime an act previously committed, which was innocent when done;
 which makes more burdensome the punishment for a crime, after its commission;
 which deprives one charged with crime of any defense available according to the law at the time when the act was committed.
" the Collins court also supplied an abbreviated formulation of the rule: "Legislatures may not retroactively alter the definition of crimes or increase the punishment for criminal acts." (Id. at p. 43.)
The Collins court explained a deprivation of a formerly available defense is "linked to the prohibition on alterations in 'the legal definition of the offense' or 'the nature or amount of the punishment imposed for its commission.'" ( Collins v. Youngblood, supra, 497 U.S. at p. 50.)