Witness interviewing and crime investigation

Witness testimony is fragile, incomplete, and malleable. It is therefore important to devise investigative and interviewing procedures which maximise the accuracy of the information elicited from a witness, whilst minimising the risk of contamination of the witness’s memory. The memory of a witness needs to be treated as though it is a part of the ‘crime scene’, which must be protected and examined in a carefully planned way. Front-line interviewing needs to be quick and effective. Any delay between encoding and retrieval of information will increase the amount of forgetting and will also increase the risk of contamination from other sources. Witnesses are likely to experience stress during a crime and this could reduce the amount of detail that they can recall. A related finding is the tendency of witnesses to suffer weapon focus. Inappropriate questioning during a witness interview can potentially contaminate the already fragile memory of a witness to crime. Witnesses to an incident or crime should be separated from each other as soon as possible and interviewed individually, to prevent cross-witness contamination. The cognitive interview (CI) is a technique which helps investigators to elicit a greater amount of information from witnesses and victims of crime, without reducing the accuracy of the information gained. The original CI comprised four main principles, which are to report everything, to mentally reinstate context, to recall events in different orders, and to change perspective. Special care needs to be taken when interviewing vulnerable witnesses, such as children, the elderly, and those with impaired mental functioning. Until recently the research findings on witness testimony and interviewing had not been widely applied in the real world. However, some countries have now introduced extensive training for police officers in these approaches, and police and researchers are increasingly working in partnership to produce evidence-based techniques.