Lynce v. Mathis

Summary

The Court held that Florida's retroactive cancellation of previously awarded prison-overcrowding credits violated the Ex Post Facto Clause by prolonging petitioner's imprisonment after those credits had secured his release. The constitutional inquiry concerns the cancellation's effect on punishment, not the legislature's purpose in originally authorizing the credits. Later modifications to the credit system did not defeat petitioner's core claim, although the Court left for remand whether some credits exceeded what the statute in effect at the time of his offense would have authorized. Justice Stevens wrote for seven Justices. Justice Thomas, joined by Justice Scalia, concurred in part and in the judgment, agreeing that cancellation of credits already earned and used was unconstitutional but declining to join the discussion of Weaver and future credits.