Article I, Section 10, Clause 1:
No State shall enter into any Treaty, Alliance, or Confederation; grant Letters of Marque and Reprisal; coin Money; emit Bills of Credit; make any Thing but gold and silver Coin a Tender in Payment of Debts; pass any Bill of Attainder, ex post facto Law, or Law impairing the Obligation of Contracts, or grant any Title of Nobility.
An accused person does not have a right to be tried in all respects in accordance with the law in force when the crime charged was committed. 1 Laws shifting the place of trial from one county to another, 2 increasing the number of appellate judges and dividing the appellate court into divisions, 3 granting a right of appeal to the state, 4 changing the method of selecting and summoning jurors, 5 making separate trials for persons jointly indicted a matter of discretion for the trial court rather than a matter of right, 6 and allowing a comparison of handwriting experts, 7 have been sustained over the objection that they were ex post facto. It was suggested in a number of these cases, and two decisions were rendered precisely on the basis, that the mode of procedure might be changed only so long as the
substantial rights of the accused were not curtailed. 8 The Court has now disavowed this position. 9 All that the language of most of these cases meant was that a legislature might not evade the ex post facto clause by labeling changes as alteration of
procedure. If a change labeled
procedural effects a substantive change in the definition of a crime or increases punishment or denies a defense, the clause is invoked; however, if a law changes the procedures by which a criminal case is adjudicated, the clause is not implicated, regardless of the increase in the burden on a defendant. 10
Changes in evidentiary rules that allow conviction on less evidence than was required at the time the crime was committed can also run afoul of the ex post facto clause. This principle was applied in the Court's invalidation of retroactive application of a Texas law that eliminated the requirement that the testimony of a sexual assault victim age 14 or older must be corroborated by two other witnesses, and allowed conviction on the victim's testimony alone. 11