Police detectives

SIGNIFICANCE: Trained detectives increase the effectiveness of police efforts to solve crimes. As specialists in the art and science of criminal investigation, they help to ensure professional and thorough responses to serious crimes.

Glorified in fiction and essential in fact, detectives are both common and crucial figures in American law enforcement. Although full-time police detectives are not nearly as numerous as uniformed patrol officers, they can be found in almost all large and medium-sized police departments. Although the popular image of police detectives is of plainclothes officers assigned full time to criminal investigative work, almost all police officers perform at least some detective work in the course of their routine duties.

History

The development of professional police detectives is closely linked to crimes that could not be prevented or deterred by uniformed patrol officers. When the first American police departments began forming in the early nineteenth century, they consisted only of uniformed patrol officers. Over time, it became obvious that crimes were continuing to occur despite the work of routine police patrols and that methods of investigating crimes after they occurred was necessary.

In England and France, criminals known as “thief catchers” were used by police forces to help catch other criminals, as it was believed that only criminals themselves could know enough about the habits of criminals to solve crimes. However, that method of crime detection failed—primarily because of the dishonesty of the thief catchers themselves—so agencies began experiments using sworn police officers as investigators of crimes. The London Metropolitan Police pioneered the use of plainclothes detectives in the mid-nineteenth century. These detectives were stationed in a London building that had been formerly used by Scottish royalty, and their work was closely followed by the press and by the novelist Charles Dickens, who wrote positive articles about the detectives who came to be known as “Scotland Yard,” or “the Yard,” after their headquarters. In addition to writing about the detectives’ heroic work, Dickens coined the term detective in his 1853 novel Bleak House.

In the United States, detectives began appearing in police departments during the 1840s, most notably in Boston, Chicago, and New York City. By the end of the Civil War, in 1865, nearly all large American cities had detective units. Many of them were kept busy by a postwar crime wave and problems of urban overcrowding brought on by new waves of European immigration. Some detectives became well known as newspapers closely followed their exploits.

New York City’s Inspector Thomas Byrnes promoted the theory of modus operandi (MO), which was based on the principle that individual criminals tend to use the same methods of operation in their crimes and that recognizing those distinctive methods can help identify the perpetrators of crimes. In 1886, Byrnes published a book detailing the methods of hundreds of felons then active along the East Coast.

In contrast to those in Europe, American private detectives rivaled public detectives in popularity and effectiveness. Allan Pinkerton emerged as the country’s foremost private detective, setting an example that was copied by many police investigators. In addition to establishing a series of highly profitable private detective branch offices across the country, Pinkerton also served as Chicago’s first public detective and headed the US Secret Service during the Civil War.

During the twentieth century, the development of motor vehicle transportation and the rise of statewide crime rings promoted the creation of state police and highway patrols with detective units of their own. Meanwhile, a number of specialized federal offices of criminal investigation arose during the late nineteenth and early twentieth centuries. In addition to the Secret Service, these included the US Customs Service, the Bureau of Investigation—which later became Federal Bureau of Investigation (FBI)—and the Internal Revenue Service (IRS).

Types of Detectives

The largest numbers of full-time, plainclothes detectives are found in local law-enforcement agencies. In 2020, approximately 13 percent of all sworn police officers were detectives or investigators. The New York City Police Department had the largest number of detectives of any single agency, with 5,221 in 2024; the FBI had the most federal investigators, with about 10,100 in 2018. In 2019, according to the Bureau of Labor Statistics, there were 105,620 detectives and criminal investigators working at state, local, and federal law-enforcement agencies, illustrating the continued need for these professionals in the modern criminal landscape.

Most city, county, and state detectives are selected from among officers already working in regular patrol divisions. Unlike many European police departments that allow college graduates to begin their police careers as investigators, most American agencies regard patrol work to be an invaluable part of the maturing and learning process that officers should have before becoming detectives. Although some federal criminal investigators have prior patrol experience, it is not required for federal special agent positions.

In addition to sworn police officers, thousands of other government investigators and private detectives also do detective work in the United States. Investigators who assist public defenders’ offices and coroners, and other government employees who perform state and federal background applicant checks, are also numerous. The numbers of private detectives vary considerably from state to state, with more than thirty-eight thousand employed throughout the country in 2022, according to the Bureau of Labor Statistics.

Police Detective Duties

Crime cases come to the attention of police agencies through three channels: victim and witness reporting, patrol observation, and initiatives undertaken by investigators. The majority of cases are reported by the general public. After they are reported, cases are assigned to individual detectives either through systems of rotation or because of the detectives’ investigative specialties. Although most detectives are able to investigate all types of crime, individual detectives tend to specialize. Some concentrate on violent crimes, others on serial crimes, high-loss property offenses, or cases involving unidentified perpetrators.

Criminal investigations are typically divided into three phases: preliminary investigations; continuing, or follow-up, investigations; and concluding investigations. Preliminary investigations focus on processing crime scenes and the initial interviewing of victims and witnesses. Often completed by regular patrol officers, the preliminary investigations serve as case foundations.

In larger police agencies, continuing and concluding investigations are undertaken exclusively by detectives. Continuing investigations seek to establish the identities of suspects, find new victims and witnesses, and coordinate evidence processing with crime laboratories. During the concluding phase, decisions must be made whether to suspend the cases or prepare them for prosecution.

Success rates of detective work vary with the types of crimes. The FBI reported that in 2019, the last year for which data is available, 45.5 percent of violent crimes and 17.2 percent of property crimes were cleared by arrest or exceptional means. Examples of the latter include death of the suspect and the victim's refusal to cooperate.

Traits of the Detective

Certain personality traits appear to be important to successful detective work. For example, an ability to reason logically and objectively is essential. Deductive and inductive reasoning are both commonly employed in detective work. Detectives employing the deductive method form their general conclusions before all facts are explained and then use additional facts to modify or verify those conclusions. Detectives using the inductive method wait for all relevant facts and information to emerge before drawing any conclusions. The inductive method is most commonly used in complex white-collar crimes and drug cases involving many suspects.

Other traits essential to proper detective work include strong organizational ability, heightened observational skills, ability to communicate with a wide variety of people, advanced search and seizure legal knowledge, and a thorough understanding of forensic science capabilities.

Bibliography

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