The nature of the contributions psychologists can make becomes clear from a recognition that the challenges police face during the course of investigations are readily conceptualised as a series of decision-making tasks. These tasks can be derived from consideration of the sequence of activities that constitute the investigative process, from the point at which a crime is committed through to the bringing of a case to court. As they progress through this sequence of activities, detectives reach choice points, at which they must identify the possibilities for action on the basis of the information they can obtain. For example, when a burglary is committed they may seek to match fingerprints found at the crime scene with known suspects. This is a relatively straightforward process of making inferences about the likely culprit from the information drawn from the fingerprint. The action of arresting and questioning the suspect follows from this inference.
However, in many cases the investigative process is not so straightforward. Detectives may not have such clear-cut information but, for example, suspect that the style of the burglary is typical of one of a number of people they have arrested in the past. Or, in an even more complex example, such as a murder, they may infer from the disorder at the crime scene that the offender was a burglar disturbed in the act. These inferences will either lead them on to seek other information or to select from a possible range of actions, including the arrest and charging of a likely suspect.
Investigative decision-making thus involves the identification and selection of options, such as possible suspects or possible lines of enquiry, which will lead to the eventual narrowing down of the search process. In order to generate possibilities and select from them, detectives and other investigators must draw on some understanding of the actions of the offender(s) involved in the offence they are investigating. They must have some idea of typical ways in which offenders behave that will enable them to make sense of the information obtained. Throughout this process they must amass the appropriate evidence to identify the perpetrator and prove their case in court.
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