Our review of whether the ex post facto clauses of the Montana and United States Constitutions are implicated in a criminal case is plenary, meaning we simply determine whether the District Court's interpretation of the law is correct. State v. Anderson, 2008 MT 116, ¶ 18, 342 Mont. 485, 182 P.3d 80.
Whether the ex post facto clauses of the federal and Montana Constitutions are implicated in charging a criminal offense is a question of law. State v. Brander, 280 Mont. 148, 150, 930 P.2d 31, 33 (1996).