Organization of detectives
The detective branch in most larger 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:
Techniques of detectives
Street work
Detectives have a wide variety of techniques available in conducting investigations. However, the majority of cases are solved by the interrogation of suspects and 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.
In criminal investigations, once a detective has a suspect or 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 in exchange for a plea bargain for a lesser sentence. A detective may lie or otherwise mislead and may psychologically pressure a suspect into confessing, though in the United States suspects may invoke their Miranda rights.
Forensic evidence
Physical forensic evidence in an investigation may provide leads to closing a case.
Examples of physical evidence can be, but are not limited to:
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Fingerprinting of objects persons have touched
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DNA analysis
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Luminol to detect blood stains that have been washed
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Bloodstain pattern analysis
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Footprints or tire tracks
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Chemical testing for the presence of narcotics or expended gun propellant
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Many major police departments in a city, county, or state, and the Federal Bureau of Investigation , maintain their own forensic laboratories.
Records investigation
Detectives may use public and private records to provide background information on a subject. These include:
Fingerprint records. In the United States, the FBI maintains records of people who have committed felonies and some misdemeanors, all persons who have applied for a Federal security clearance, and all persons who have served in the U.S. armed forces
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Records of criminal arrests and convictions
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Photographs or mug shots, of persons arrested
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Motor vehicle records
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Credit card records and bank statements
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Hotel registration cards
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Credit reports
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Answer machine messages
Court testimony
Unless a plea bargain forestalls the need for a trial, detectives must testify in court about their investigation . They must seem reliable and credible to a jury, and must not give the impression of personal vindictiveness or cruelty. A detective's background often comes into question in courtroom testimony. A famous example came in the murder trial of O. J. Simpson, when Detective Mark Fuhrman of the Los Angeles Police Department testified for the prosecution. Attorney F. Lee Bailey first asked Fuhrman if he had ever used the "n-word" (see Nigger) Fuhrman denied this. In court, Bailey produced taped interviews with Fuhrman using this offensive word.
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