Definition
An informer is a person who reports another's suspected violation of a penal statute to law enforcement or judicial authorities, typically to trigger a prosecution. The term carries two distinct but related meanings in legal usage:
1. General informer. Any person who supplies information to authorities about criminal conduct — whether a private citizen, a witness, or a confidential source used by police or prosecutors. In this sense, the informer is an evidentiary and investigative figure whose identity and reliability become issues in criminal proceedings.
2. Common informer. A person who, without any official duty or special injury to themselves, habitually discovers penal violations and initiates prosecutions — often because the applicable statute awards a share of any resulting penalty to whoever brings the action. This is the technically precise legal meaning that historical sources emphasize. The common informer acts not from civic grievance but from financial incentive, suing under statutes that reward "any person" who prosecutes (qui tam actions). The common informer is distinct from a party who is specially aggrieved by the offense and who sues to vindicate a personal injury.
Common Language
Modern common usage (Wiktionary): One who informs someone else about something; a person who tells authorities about improper or illegal activity.
Historical common usage (Webster's 1913): One who imparts knowledge or news; one who informs a magistrate of violations of law; one who informs against another for violation of some law or penal statute.
The common and legal meanings overlap substantially, but the legal tradition draws a sharper internal distinction between the general informer and the common informer than ordinary usage suggests. Colloquially, "informer" carries a strong connotation of betrayal or collaboration with law enforcement — a snitch or mole inside a criminal organization. The legal term, particularly in its historical usage, is at least as concerned with the bounty-hunting common informer exploiting penal statutes for profit as with the covert police informant. These are functionally very different figures, and conflating them produces research errors when reading older sources.
Common Confusion
Informer vs. Informant: In modern criminal law and police practice, "informant" has largely displaced "informer" to describe the covert source — a person with insider knowledge of criminal activity who supplies information to law enforcement, often under promises of leniency or payment. "Informer" in this modern sense is used interchangeably, but historical legal sources use "informer" almost exclusively and may not use "informant" at all. Researchers moving between historical and modern materials must track this terminological drift. Additionally, neither term should be confused with a complainant or a whistleblower, though there is conceptual overlap with the latter in qui tam contexts.
Informer vs. Promoter: Burrill notes that the informer was also called "promoter" in old law. In modern usage, "promoter" has an entirely different legal meaning (securities and corporate law). Encountering "promoter" in historical materials about criminal or penal procedure requires attention to context.
Recognized Forms
/SUBTYPES
Common Informer. The formally recognized subtype appearing in all historical sources. Defined as one who habitually ferrets out penal violations and initiates prosecution for personal gain — specifically, to collect a statutory reward or share of penalty — rather than from official duty or personal grievance. Associated with qui tam actions. The common informer figure was widely disfavored in equity and eventually abolished or severely restricted in England by statute (Common Informers Act 1951) and was never robustly embraced in American federal practice, though qui tam mechanisms survive in the False Claims Act context.
Confidential Informer (CI). The modern law enforcement usage. A person — often embedded in or associated with criminal activity — who provides information to police or prosecutors, typically under conditions of anonymity. The CI's identity, reliability, and the information supplied raise Fourth Amendment, Sixth Amendment Confrontation Clause, and due process issues in criminal proceedings. This subtype is almost entirely absent from historical legal dictionaries, which were written before the modern era of systematic police use of confidential sources.
Why It Matters in Research
The term "informer" sits at the intersection of two largely separate bodies of law that historical dictionaries treat as a single concept: the qui tam/common informer tradition and the modern confidential informant doctrine. Researchers must identify which is relevant before trusting a source's definition.
In historical sources (pre-20th century), "informer" almost always means the common informer in the penal statute sense. The competency of the informer as a witness — addressed by Bouvier with citations to Phillips and Roscoe on evidence — was a live question because the informer had a financial stake in conviction. This evidentiary competency issue is effectively obsolete in modern practice but will appear throughout 18th and 19th century English and American case law.
In modern criminal law research, the operative figure is the confidential informant, governed by a body of constitutional doctrine (Roviaro v. United States on the informer's privilege; Fourth Amendment probable cause based on informant tips under the Aguilar-Spinelli test and its successor Gates totality standard). None of this appears in the historical dictionaries. Researchers using Black's or Bouvier's to understand informer doctrine in a modern criminal context will find the entries largely beside the point.
The qui tam connection is significant for civil researchers. The False Claims Act's qui tam provisions are the surviving American descendant of the common informer mechanism. Researchers working on whistleblower or False Claims Act matters will find the historical common informer literature useful as intellectual background, though the modern statutory framework has superseded it.
Jurisdictional variation is real: some states have their own qui tam or informer-reward statutes with independent interpretive traditions. The competency-as-witness issue, though obsolete federally, may linger in state statutory frameworks built on older models.
Historical Dictionary Support
All four sources agree on the basic definition: an informer is one who reports another's suspected penal violation to set a prosecution in motion. The entries are substantially consistent, differing mainly in elaboration.
Black's (both editions) and Bouvier's emphasize the common informer as the core legally significant subtype, with Black's 1st edition offering the clearest functional definition by contrasting the common informer (who sues for a penalty available to anyone) with a specially aggrieved party. Burrill adds the useful historical synonyms — informator, delator, promoter — which alert researchers to variant terminology in Latin legal sources and old English law. Bouvier goes furthest in addressing the evidentiary question of the informer's competency as a witness, reflecting that this was a practically contested issue in 19th-century courts.
What the historical dictionaries collectively miss: the confidential police informant, informant privilege doctrine, and the constitutional framework governing use of informant-supplied information in establishing probable cause. These developed almost entirely in the 20th century and require modern sources. The historical dictionaries also do not address the subsequent legislative abolition or restriction of the common informer in England, or the transformation of the qui tam mechanism in American statutory law.
Jurisdictional Note
The common informer mechanism was effectively abolished in England by the Common Informers Act 1951 but survives in American federal law through the False Claims Act's qui tam provisions and scattered state analogs. Modern confidential informant doctrine is primarily federal constitutional law but is applied in all jurisdictions; state courts may provide broader protections than federal minimums, particularly on disclosure of informant identity.
Encyclopedia Cross-Reference
The Law Mind Criminal Law Encyclopedia: Sixth Amendment — Right to Be Informed of Charges (criminal_185) — relevant for the intersection of informer-supplied accusations and defendants' rights to know the basis of charges against them.