Crime Detection

I

Introduction

Crime Detection, discovery, identification, and analysis of criminal evidence as a means of law enforcement. The responsibility of law enforcement agencies is to detect crimes, apprehend the perpetrators, and provide evidence that will convince judges and juries that the perpetrators are guilty beyond a reasonable doubt. To accomplish these aims a variety of methods are used, including reconstructing the crime, collecting physical clues, and interrogating suspects and witnesses.

The methods of detection employed are dictated by the nature of the crime and the procedures permitted by the legal system. Most investigations begin with careful, objective observations that are then assembled, collated, and matched against applicable law. If there is reason to assume that a crime has indeed been committed, further investigation is undertaken using scientific methods and techniques. Technological advances have been incorporated into criminal investigation as well; for example, analyzing trace clues such as dust, paint, glass, and other microscopic evidence is now possible.

II

Historical Background

Early criminal investigation was a crude process, relying on eyewitnesses, inferences, and confessions extracted under torture. In early 19th-century France, for instance, the principal technique for catching thieves was obtaining evidence from informers who were also engaged in crime.

The first major step in modern crime detection took place in Great Britain. In 1829 the Metropolitan Police Act established the basis for the world-famous Scotland Yard detective department (see Scotland Yard), which investigated crimes in London and, occasionally, throughout the British Empire. The British example influenced the development of criminal investigation in the United States, where large cities patterned their police efforts after the successful model in England.

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Criminal investigations are now conducted in the U.S. at municipal, state, and federal levels in accordance with the dictates of the law. The conduct of an investigation is governed by information obtained from people, records, and physical evidence. Victims or witnesses still provide the bulk of facts as to when, where, how, why, and by whom the crime was committed.

III

Surveillance

One of the oldest ways of detecting criminal activity is through surveillance. This method is used when it is likely that a crime will take place at a specific location or when certain persons are suspected of criminal activity. The first situation usually is handled by fixed police observation known as a stakeout; the second circumstance may require mobile observation as well, perhaps on foot or by automobile. Some situations may call for aerial observation (using aircraft) or electronic procedures (using surveillance equipment that monitors electronic communication).

The observation method must be legal. Surveillance techniques, for example, may include placing personnel in strategic locations and equipping them with optical aids, such as binoculars or scopes with the capacity to detect an object illuminated only by moonlight, or with electronic devices, sensitive to a conversation taking place at a considerable distance. Where a possibility exists of invasion of privacy, a court order is required to make the police action and the information obtained acceptable at a trial.

Allied to surveillance are covert or undercover observations, which usually are confined to activities such as gambling, dealing in narcotics, and other major organized crimes. Informants are the source of much useful information in investigations; they may be citizens motivated by civic duty or sometimes, criminals motivated by self-interest.

IV

Interrogation

The information needed to further an investigation must be obtained from people who have some significant knowledge concerning the crime. Witnesses or victims are interviewed, and suspects are interrogated. Eyewitnesses to a crime are often asked to identify the perpetrator, although identification errors have prompted psychologists to explore the processes and pitfalls of memory, recall, and recognition. Experiments under controlled conditions indicate that jurors will convict four times as often if eyewitness testimony is offered, even when the visual acuity of the witness is discredited. Eyewitness identifications, therefore, must be considered carefully, and the credibility of the identification must be tested to ensure that error is unlikely.

Interrogation is used when the information sought is not readily forthcoming, perhaps because of hostility or guilt. Often some key to the solution of a crime, such as the location of the weapon in a murder case, is known only to the perpetrator. Without information provided by the suspect, a crime may go unsolved. Legal safeguards against abuse now surround this process. Before using any information obtained from an interrogation, the court must be assured that the suspect was advised of his or her rights. If proper legal procedures are not followed, any evidence obtained is inadmissible in a trial.

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