In Abney v. United States, 431 U.S. 651 (1977), the Supreme Court held that an interlocutory order denying a motion to dismiss an indictment on double jeopardy grounds came under the "collateral order" exception to the final-judgment rule and, thus, was a "final decision" within the meaning of section 1291 of title 28 of the United States Code. (Abney, supra, 431 U.S. at p. 662.)
The Supreme Court found that the order denying the defendants' motion was a "fully consummated decision" (id. at p. 659); there were no further steps (other than moving for reconsideration) that could be taken in district court to avoid trial on double jeopardy ground; that the double jeopardy issue was collateral to and separable from the principal issue--whether defendant was guilty and that the rights conferred by the double jeopardy clause would be significantly undermined if the appeal were postponed. (The double jeopardy clause protects not only against being punished a second time but also "against being twice put to trial for the same offense.") (Abney, supra, 431 U.S. at p. 661.)
The court in Abney makes clear "there is no constitutional right to an appeal" and the right to an appeal in criminal cases "is purely a creature of statute." (Abney, supra, 431 U.S. at p. 656.) Abney involved the interpretation of a federal statute which provided for appeal from "final decision" (28 U.S.C. § 1291). The Supreme Court observed that the preferred procedural vehicle for review of a double jeopardy claim was a pretrial writ of habeas corpus because:
The rights conferred on a criminal accused by the Double Jeopardy Clause would be significantly undermined if appellate review of double jeopardy claims were postponed until after conviction and sentence.
To be sure, the Double Jeopardy Clause protects against being twice convicted for the same crime, and that aspect of the right can be fully vindicated on appeal following final judgment, as the Government suggests. However, the Court has long recognized that the Double Jeopardy Clause protects an individual against more than being subjected to double punishments.
It is a guarantee against being twice put to trial for the same offense. 431 U.S. at 660-61.