Eyewitnesses and the use and application of cognitive theory

Abstract

Eyewitnesses carry out a range of tasks to help the police bring a criminal to justice. They describe what happened during the crime and the people involved. Later, there may be reasonable grounds for the police to believe they know who is responsible for the offence and this person then becomes a suspect. The police may put the suspect into a line-up or identification parade and ask eyewitnesses to see if they recognise the person they saw. If the suspect is picked out, this outcome is taken as evidence that the police have arrested the correct person. The police may then spend time building a case to convict the suspect, or dismiss him or her as either there is a lack of evidence to convict or another person is responsible for the crime. Eyewitnesses also provide testimony in a court of law.

The police may use the description of an offender given by an eyewitness to try to locate this person using computer searches of previously convicted people. If a suspect cannot otherwise be identified, such as by using CCTV, DNA, fingerprints or other forensic evidence, eyewitnesses may construct a picture of the offender's face, an image called a facial composite. The police will usually circulate this image internally to police staff; if this does not identify the culprit, the image is often published on police websites, in newspapers, and on TV news and crime programmes in the hope that a member of the public will recognise the image and come forward with a name. Sometimes, the police try to establish identity by circulating a wanted poster; see Figure 12.1 for an example.

The focus of this chapter is on the various types of evidence from eyewitnesses. There have been many cases of wrongful conviction, as illustrated later by the conviction of Laszlo Virag, and these woeful outcomes must be minimised. The chapter is guided by the wealth of psychological research that has attempted to understand and improve the performance of human memory. It will be seen that eyewitness evidence, in conjunction with other evidence, is crucial for the identification and reliable conviction of offenders.

To summarise:
1. Eyewitnesses help the police bring an offender to justice.
2. Eyewitnesses give a description of crimes, take part in identification procedures, construct facial composites, and give testimony in a court of law.
3. The police may make a public appeal for information.
4. When there is good reason to believe that a person has committed an offence, he or she becomes a suspect in a criminal investigation.