The Double Jeopardy Clause in the Fifth Amendment to the United States Constitution prohibits any person from being prosecuted twice for substantially the same crime. The relevant part of the Fifth Amendment states that “nor shall any person be subject for the same offence to be twice put in jeopardy of life or limb.” The Double Jeopardy Clause applies against both state and federal governments. See Benton v. Maryland, 395 U.S. 784 (1969).

But under the “dual-sovereignty doctrine” or “separate sovereigns doctrine” the prohibition on double jeopardy does not prevent dual prosecutions when the prosecutions are conducted by separate sovereigns (governments). For example, if a person engages in criminal conduct that constitutes a crime under both state and federal law—or that constitutes a crime in two different states—the person may be prosecuted by both sovereigns without violating the Double Jeopardy Clause. See Gamble v. United States, 139 S.Ct. 1960 (2019).

The dual-sovereignty doctrine is not an exception to the prohibition on double jeopardy—rather, it follows from the Fifth Amendment's text. The Double Jeopardy Clause protects individuals from being “twice put in jeopardy” “for the same offence.” As originally understood, an “offence” is defined by a law, and each law is defined by a sovereign. Thus, where there are two sovereigns, there are two laws and two “offences.”

In Connecticut, as in all states, the Double Jeopardy Clause of the Fifth Amendment protects individuals from being tried twice for the same offense. This means that a person cannot be prosecuted again for the same conduct if they have already been acquitted or convicted, or if they have faced jeopardy in a previous trial for the same offense. However, the dual-sovereignty doctrine allows for separate prosecutions by different sovereigns, such as state and federal governments, without violating the Double Jeopardy Clause. This is because each sovereign has its own set of laws, and an offense is defined by the law of the sovereign. Therefore, if a person's actions violate both state and federal laws, or the laws of two different states, they may face prosecution by each sovereign for what are considered separate offenses. The U.S. Supreme Court reaffirmed this principle in the case of Gamble v. United States in 2019.