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A detective is an investigator, either a member of a police agency or a private person. The latter may be known as private investigators or "private eyes". Informally, and primarily in fiction, a detective is any licensed or unlicensed person who solves crimes, including historical crimes, or looks into records.
In some police departments, a detective position is not appointed, it is a position achieved by passing a written test after a person completes the requirements for being a police officer. Prospective British police detectives must have completed at least two years as a uniformed officer before applying to join the Criminal Investigation Department. UK Police must also pass the National Investigators' Examination in order to progress on to subsequent stages of the Initial Crime Investigators Development Programme in order to qualify as a Detective.
In many other police systems, detectives are college graduates who join directly from civilian life without first serving as uniformed officers. Some people argue that detectives do a completely different job and therefore require completely different training, qualifications, qualities and abilities than uniformed officers. The opposing argument is that without previous service as a uniformed patrol officer, a detective cannot have a great enough command of standard police procedures and problems and will find it difficult to work with uniformed colleagues.
Before becoming a detective, one must attend a law enforcement academy, providing the officer with a foundation of education with sixteen to twenty-four college units in criminal justice or administration of criminal justice. After graduation from the law enforcement academy the officer undergoes job training with a field training officer for a period specified by the law enforcement agency and continues to work while on a probationary period, ranging from one to two years.
During the probationary period, the officer is assigned to look for evidence, such as what color the crime scene is. During this time, the officer is supervised and mentored by a sergeant with years of experience. Some officers further their college education by attending a two-year or four-year college or university, attaining a degree in criminal justice or administration of criminal justice. Colleges have options for a concentration or certificate in a specialized field of criminal investigation.
Through years of on the job training, college education, officers may participate in a competitive examination, testing their knowledge, skills and abilities regarding criminal investigation, criminal procedure, interview and interrogation, search and seizure, collection and preservation of evidence, investigative report writing, criminal law, court procedure, and providing testimony in court. Competitive examinations are conducted by a selected senior law enforcement officials. Following testing, a list of results is provided by the department. At the department's discretion, some, or all, of the officers on the list are promoted to the rank of detective. Some departments have classes of detectives which increase the detective's rank after successful experience.
Private investigators are licensed by the state in which they work. Some states do not require licensing, but most do. In addition to the state examination, applicants testing for a private investigation license must also meet stringent requirements which include college education, a range of two to four years of full-time investigation experience, and the successful adjudication of a criminal and civil background check conducted by state investigators. Private investigators are licensed to conduct civil and criminal investigations in the state they are licensed. They are protected by statutes of the state they are licensed. In states requiring licensure, there are statutes making it unlawful for any person to conduct a criminal investigation unless they are licensed by the state, or exempt by the statute (i.e. law enforcement officers or agents, attorneys, paralegals, claims adjusters).
The detective branch in most large police agencies is organized into several squads or departments, each of which specializes in investigation into a particular type of crime or a particular type of undercover operation, which may include: homicide; robbery; burglary; auto theft; organized crimes; missing persons; juvenile crime; fraud; narcotics; vice; criminal intelligence; aggravated assault/battery; sexual assault; computer crime; domestic violence; surveillance; and arson, among others.
In some countries, the practice of a detective is not yet recognized in courts and judicial processes.
One of these countries is Portugal, where the proof presented loses all the significance when collected by a private detective. Even under this circumstance, the practice of this activity is in demand, and ruled by a code of conduct.
Detectives have a wide variety of techniques available in conducting investigations. However, the majority of cases are solved by the interrogation of suspects and the interviewing of witnesses, which takes time. Besides interrogations, detectives may rely on a network of informants they have cultivated over the years. Informants often have connections with persons a detective would not be able to approach formally. Evidence collection and preservation can also help in identifying a potential suspect(s).
Criminal investigation: the investigation of criminal activity is conducted by the police. Criminal activity can relate to road use such as speeding, drunk driving, or to matters such as theft, assault, fraud, etc. When the Police have concluded their investigation a decision on whether to charge somebody with a criminal offence will often be made by prosecuting counsel having considered the evidence produced by the Police.
In criminal investigations, once a detective has suspects in mind, the next step is to produce evidence that will stand up in a court of law. The best way is to obtain a confession from the suspect; usually, this is done by developing rapport and at times by seeking information in exchange for potential perks available through the Attorney's Office, such as entering for a lesser sentence in exchange for usable information. Detectives may lie, mislead and psychologically pressure a suspect into an admission or confession as long as they do this within procedural boundaries and without the threat of violence or promises outside their control.
Physical forensic evidence in an investigation may provide leads to closing a case. Forensic science (often shortened to forensics) is the application of a broad spectrum of sciences to answer questions of interest to the legal system. This may be in relation to a crime or to a civil action. Many major police stations in a city, county, or state, maintain their own forensic laboratories.
Detectives may use public and private records to provide background information on a subject. Police detectives can search through files of fingerprint records. Police maintain records of people who have committed felonies and some misdemeanors. Detectives may search through records of criminal arrests and convictions, photographs or mug shots, of persons arrested, and motor vehicle records.
With a search warrant, police detectives can also search through credit card records and bank statements, hotel registration information, credit reports, answer machine messages, phone conversations, and technology used for communication.