The great migration from the tsarist empire, sparked by the assassination of Alexander II, in 1881, saw two to three million east European Jews re-settling in the great cities of the Atlantic world before the First World War. Often discriminated against in labour markets, and socially marginalized in new environments, Russo-Polish males either persisted in, or resorted to, organized crime centred on the illicit sale of alcohol, professional gambling, and prostitution to survive. Atlantic states, however, were reluctant to employ Jews as uniformed police or detectives in their fight against syndicated crime. In order to overcome the challenge of ethnicized crime, law-enforcement agencies, like nineteenth-century tsarist administrations before them, employed informers. Jewish informers who, unbeknown to police handlers, were sometimes also psychopaths in an era before the condition was clinically identified, were used to infiltrate underworld structures. By nature, informing offered a short-term, unstable, existence fraught with unintended consequences for police and spies alike – thereby encouraging extraordinary geographical mobility amongst informers. Orthodox histories of law-enforcement agencies tend to focus on structural changes in police forces but a re-examination of the role of informers in organized crime should allow for the development of more subtle insights into the evolution of policing as a dynamic, interactive, social process.