Definition
Once in jeopardy is a phrase describing the legal condition of a person who has already been subjected to criminal proceedings for a particular offense in a manner that triggers constitutional or common law protection against a second prosecution for that same offense. When a defendant has been "once in jeopardy," the constitutional bar against double jeopardy attaches, and any subsequent prosecution for the same offense is prohibited.
The phrase is not itself a standalone doctrine but rather a shorthand for the threshold question in double jeopardy analysis: has jeopardy attached? Until jeopardy attaches — a moment determined by procedural rules that vary by context — the protection does not operate. Once it does attach and the proceeding concludes (by acquittal, conviction, or in some circumstances mistrial), the defendant has been "once in jeopardy" and cannot be tried again for the same offense.
Common Confusion
Once in jeopardy is closely related to, but should not be conflated with, three distinct concepts:
AUTREFOIS ACQUIT and AUTREFOIS CONVICT are the formal common law pleas a defendant enters to raise the double jeopardy bar. "Once in jeopardy" describes the condition that gives rise to those pleas; the pleas are the procedural mechanism for asserting it.
JEOPARDY (attachment) is the moment-focused inquiry — when did jeopardy first attach? "Once in jeopardy" presupposes that attachment has already occurred and asks whether the concluded proceeding now bars a new one. Researchers conflating the two may misread historical sources that treat "jeopardy" and "once in jeopardy" as interchangeable when they are addressing different stages of the analysis.
Why It Matters in Research
The phrase functions primarily as a doctrinal marker in older common law and early American criminal law sources. Several traps await researchers:
Historical sources treat "once in jeopardy" as the operative test without fully unpacking when jeopardy attaches — a question that nineteenth-century courts answered inconsistently. Some older authorities held that jeopardy attached upon indictment; modern doctrine requires impaneling and swearing of a jury (in jury trials) or the first witness being sworn (in bench trials). Reading pre-twentieth-century cases through a modern lens will produce errors.
The phrase appears in both constitutional and common law discussions, and researchers must distinguish the two. The Fifth Amendment's Double Jeopardy Clause constitutionalized the protection federally; state protections developed independently and sometimes diverged. Pre-incorporation sources (before Benton v. Maryland applied the Double Jeopardy Clause to the states) may reflect state common law doctrine rather than federal constitutional doctrine.
Burrill's cross-reference to "once a mortgage, always a mortgage" within the same entry is not a doctrinal connection — it reflects Burrill's alphabetical structure and should not mislead researchers into treating the two maxims as related.
The Rapalje & Lawrence entry's terse cross-reference to AUTREFOIS ACQUIT, AUTREFOIS CONVICT, and JEOPARDY signals that for those compilers, "once in jeopardy" had no independent significance beyond the pleas it generated. Researchers using Rapalje & Lawrence should follow those cross-references rather than treating the entry itself as substantive.
Corpus researchers should note that "once in jeopardy" appears with greater frequency in nineteenth-century American criminal law treatises — particularly Wharton — than in modern sources, where "double jeopardy" and "jeopardy attachment" have largely displaced it as the operative vocabulary.
Historical Dictionary Support
The historical sources converge on the core meaning: a person "once in jeopardy" is one who has been placed in legal danger of conviction and punishment for an offense by a formal legal proceeding. Both editions of Black's carry nearly identical definitions, emphasizing the danger of conviction and punishment as the qualifying condition.
Burrill is the most substantive historical source, directing researchers to Wharton's American Criminal Law for the range of interpretive positions on the phrase — a signal that even by the mid-nineteenth century, "once in jeopardy" was contested rather than settled. Burrill's reference to Wharton sections 573–591 reflects genuine doctrinal uncertainty about what proceedings sufficed to put a defendant in jeopardy.
The Scotch maxim carried in both Black's editions — "once quit and cleared, ever quit and cleared" (anis quit and clenged, ay quit and clenged), attributed to Skene's De Verborum Significatione — gestures toward the common law roots of the protection across legal systems, though its presence in American dictionaries is largely ornamental.
What historical sources consistently omit: any treatment of jeopardy in the context of mistrials, hung juries, or dismissed proceedings — situations that generate the most litigation in modern double jeopardy doctrine. The historical entries assume a completed proceeding ending in acquittal or conviction, which understates the complexity researchers will encounter in case law.
Jurisdictional Note
Federal double jeopardy doctrine under the Fifth Amendment applies to the states through incorporation. However, the dual sovereignty doctrine — treated separately in the Law Mind Encyclopedia — permits successive federal and state prosecutions for the same conduct without triggering the bar. Researchers working with pre-incorporation sources must be attentive to whether a case applies state common law, a state constitutional analog, or federal doctrine.
Encyclopedia Cross-Reference
Double Jeopardy — Attachment and Scope (The Law Mind Criminal Law Encyclopedia)
Double Jeopardy — Dual Sovereignty Doctrine (The Law Mind Criminal Law Encyclopedia)