Article I, Section 9, Clause 3:
No Bill of Attainder or ex post facto Law shall be passed.
Multiple Supreme Court decisions have held that the Ex Post Facto Clauses apply only to federal and state legislation (including state constitutional amendments), not to judicial decisions.1 In Ross v. Oregon, the Court declined to apply the prohibition on ex post facto laws to a court decision that interpreted a statute that had been in place at the time of the offense to the disadvantage of the defendant.2 In Frank v. Mangum, the Court rejected an ex post facto challenge to a judicial decision that allegedly departed from precedent.3 The Court explained that the state Ex Post Facto Clause “is directed against legislative action only, and does not reach erroneous or inconsistent decisions by the courts.” 4 Similarly, in Marks v. United States, the Court held that the federal Ex Post Facto Clause “is a limitation upon the powers of the Legislature . . . and does not of its own force apply to the Judicial Branch of government.” 5
Although the Judicial Branch is not bound by the Ex Post Facto Clauses, the Court has held that the Due Process Clause might similarly prevent a defendant from being convicted for conduct that would not have been criminal but for an intervening court decision.6 In Bouie v. City of Columbia, the Supreme Court held that “an unforeseeable judicial enlargement of a criminal statute, applied retroactively, operates precisely like an ex post facto law” and “[i]f a state legislature is barred by the Ex Post Facto Clause from passing such a law, it must follow that a State Supreme Court is barred by the Due Process Clause from achieving precisely the same result by judicial construction.” 7 In Rogers v. Tennessee, the Court reiterated that while the Ex Post Facto Clause does not apply to the judiciary, “limitations on ex post facto judicial decisionmaking are inherent in the notion of due process.” 8 However, the Rogers Court also held that the due process limitation on courts is not identical to the ex post facto prohibition that applies to legislation. The Court explained:
The Ex Post Facto Clause, by its own terms, does not apply to courts. Extending the Clause to courts through the rubric of due process thus would circumvent the clear constitutional text. It also would evince too little regard for the important institutional and contextual differences between legislating, on the one hand, and common law decisionmaking, on the other.9
- See generally Cummings v. Missouri, 71 U.S. 277 (1866).
- 227 U.S. 150, 161 (1913).
- 237 U.S. 309, 344–45 (1914).
- Id. at 344.
- 430 U.S. 188, 191 (1977) (citation omitted).
- See, e.g., United States v. Marcus, 560 U.S. 258, 263 (2010) (holding that if a criminal defendant was erroneously convicted based on noncriminal conduct that preceded enactment of the relevant law, he would have a due process claim rather than an ex post facto claim).
- 378 U.S. 347, 353–354, (1964). See also Marks v. United States, 430 U.S. 188, 195–96 (1977) (applying Bouie); but see Splawn v. California, 431 U.S. 595 (1977) (rejecting application of Bouie where there was no “change in the interpretation of the elements of the substantive offense” ).
- 532 U.S. 451, 456 (2000).
- Id. at 460.