What is one constitutional limitation regarding bills that retroactively declare guilt?

The prohibition of bills that retroactively declare guilt is grounded in the principle of ex post facto laws, which are forbidden under both the U.S. Constitution and many state constitutions, including Arizona's. These laws would allow the government to impose penalties on individuals for actions that were not considered crimes at the time they were committed, undermining fundamental legal principles such as fairness and justice. This constitutional limitation ensures that individuals are protected from arbitrary retrospective punishment and promotes a stable legal framework where laws must be clear and known at the time of an action. By prohibiting such bills, the constitution aims to uphold individual rights and maintain a just legal system.