Dual sovereignty doctrine

The Double Jeopardy Clause of the Fifth Amendment to the United States Constitution provides: "[N]or shall any person be subject for the same offence to be twice put in jeopardy of life or limb . . . ." The four essential protections included are prohibitions against, for the same offense:

Jeopardy attaches in jury trial when the jury is empaneled and sworn in, in a bench trial when the court begins to hear evidence after the first witness is sworn in, or when a court accepts a defendant's plea unconditionally. Jeopardy does not attach in a retrial of a conviction that was reversed on appeal on procedural grounds (as opposed to evidentiary insufficiency grounds), in a retrial for which "manifest necessity" has been shown following a mistrial, and in the seating of another grand jury if the prior one refuses to return an indictment.

In United States v. Felix 503 U.S. 378 (1992), the U.S. Supreme Court ruled: "a[n]...offense and a conspiracy to commit that offense are not the same offense for double jeopardy purposes."

Sometimes the same conduct may violate different statutes. If all elements of a lesser offense are relied on to prove a greater offense, the two crimes are the "same offense" for double jeopardy purposes, and the doctrine will bar the second prosecution. In Blockburger v. United States, 284 U.S. 299 (1932), the Supreme Court held that "where the same act or transaction constitutes a violation of two distinct statutory provisions, the test to be applied to determine whether there are two offenses or only one, is whether each provision requires proof of an additional fact which the other does not". The test was applied in Brown v. Ohio, 432 U.S. 161 (1977), where the defendant had first been convicted of operating an automobile without the owner's consent, and later of stealing the same automobile. The Supreme Court concluded that the same evidence was necessary to prove both offenses, and that in effect there was only one offense. Therefore, it overturned the second conviction.

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