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The Psychology of Police Lineups

© Michael Decaire

Eyewitness identification of a criminal suspect can be one of the most influential factors in a criminal investigation. Two consequences can result from a eyewitness account that is accepted by an investigation, and subsequently a court of law. First,the eyewitness's information could lead to the removal from society of a dangerous and repeat offender. Secondly, a false identification could possibly lead to the incarceration of an innocent individual while the guilty party remains as a risk to the community.

One would like to believe the most identifications lead to the first result. However, history has shown that eyewitness identification is easily influenced and wrongful accusations and incarceration has resulted from these errors in memory. Psychology has now stepped into the realm of eyewitness identification in order to provide some understanding of why misidentification occurs. Secondly, the understanding of this phenonmenom that psychology has provided has allowed for a number of recommendations to possibly help eliminate false identifications.

Typically in a police line consists of a supsect placed among a series of non-suspects called distractors or foils. The individuals are placed in front of the eyewitness. Psychological thought argues that control group conditions should be used in order to maximize the effectiveness and reliability of identification.

One control condition is the blank-lineup control group. In this condition the witness would be exposed to a police lineup that does not included the suspect. This technique is presumed to identify an eyewitness who has either a poor memory of the perpetrator or who would identify an individual in the lineup based on stereotypes or what they believe the investigator is looking for. While it is deceptive the blank-lineup control is a very powerful a priori tool for identification of a witnesses response biases. An additional encouraging note is that the eyewitnesses ability to identify the suspect in a second lineup is not affected to a signficant extent by the blank lineup.

A second control condition is refered to as the mock-witness control. In which individuals who are non in reality an eyewitness to an event are exposed to a normal lineup containing the suspect. This is an a priori technique that can be quite effective in creating a valid and fair lineup. If a mock witness is able to identify the suspect at a higher rate then chance a few things may be occuring. First, it is possible that the suspect stands out from the rest of the lineup via the fullfilment of a certain stereotype of the criminal associated with this type of crime. It has actually been shown that a mock witness is able to identify the offender at a rate significantly higher then chance via a very basic description of the offender and the crime (like what people