Under the U.S. Constitution, the prohibition against ex post facto laws applies only to penal statutes. See Weaver v. Graham, 450 U.S. 24, 101 S. Ct. 960, 67 L. Ed. 2d 17 (1981).
Under the Colorado constitution, ex post facto analysis is limited to criminal cases.
However, in the civil context, Colorado courts have considered ex post facto challenges under the Colorado constitution based on a retrospective statute analysis. See Gasper v. Gunter, 851 P.2d 912 (Colo. 1993).
A statute is presumed to be constitutional and the burden is on the party attacking the statute to establish its unconstitutionality beyond a reasonable doubt. People in Interest of C.M., 630 P.2d 593 (Colo. 1981).
A statute is not unconstitutional merely because the facts upon which it operates occurred before the adoption of the statute. People v. D.K.B., 843 P.2d 1326 (Colo. 1993). Nor does the modification of the remedy for collection of past-due support impair a vested right that belongs to father. See Ficarra v. Department of Regulatory Agencies, 849 P.2d 6 (Colo. 1993) (vested right must be more than a mere expectation based upon an anticipated continuance of existing law); Colorado Department of Social Services v. Smith, Harst & Associates, Inc., 803 P.2d 964 (Colo. 1991) (a vested right in remedies does not exist).