Ellingburg v. United States · ¶59

Whether a law is subject to the Ex Post Facto Clauses will therefore typically depend on how it is enforced. If it is enforced on behalf of the sovereign to redress a sovereign injury, then it is subject to the Clauses. See 4 Blackstone 2. If instead it is enforced by a private person to vindicate his own private rights, then it is not. In this case, for example, the law was subject to the Ex Post Facto Clauses because it was enforced against Ellingburg by the United States, not by the First Union National Bank, whose private rights Ellingburg violated when he robbed it. And the United States's action was redressing a sovereign injury to the community as a whole, not a private wrong. Cf. 3 Blackstone 257 (explaining that the King can bring “common law actions” to redress private wrongs to himself, such as an “action for trespass for taking away his goods”).

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