The National Institute of Justice: Police lineups; making eyewitness identification more reliable.

At its most basic level, a police lineup involves placing a suspect among people not suspected of committing the crime (fillers) and asking the eyewitness if he or she can identify the perpetrator. This can be done using a live lineup of people or, as more commonly done in U.S. police departments, a lineup of photographs. Live lineups typically use five or six people (a suspect plus four or five fillers) and photo lineups six or more photographs.

There are two common types of lineups: simultaneous and sequential. In a simultaneous lineup (used most often in police departments around the country),the eyewitness views all the people or photos at the same time. In a sequential lineup, people or photographs are presented to the witness one at a time.

Live Police Lineups: How Do They Work?

Typically, the law enforcement official or lineup administrator knows who the suspect is. Experts suggest that lineup administrators might—whether purposefully or inadvertently—give the witness verbal or nonverbal cues as to the identity of the suspect. For instance, if an eyewitness utters the number of a filler, the lineup administrator may say to the witness, “Take your time . . . . Make sure you look at all the photos.” Such a statement may effectively lead the witness away from the filler. In a “double-blind” lineup, however, neither the administrator nor the witness knows the identity of the suspect, and so the administrator cannot influence the witness in any way.

Additional variables that can affect the outcome of police lineups include:

Prelineup instructions given to the witness. This includes explaining that the suspect may or may not be present in the lineup. Research on prelineup instructions by Nancy Steblay, Ph.D., professor of psychology at Augsburg College in Minneapolis, Minnesota, revealed that a “might or might not be present” instruction reduced mistaken identification rates in lineups where the suspect was absent.

The physical characteristics of fillers. Fillers who do not resemble the witness’s description of the perpetrator may cause a suspect to stand out.

Similarities or differences between witness and suspect age, race, or ethnicity. Research suggests that when the offender is present in a lineup, young children and the elderly perform nearly as well as young adults in identifying the perpetrator. When the lineup does not contain the offender, however, young children and the elderly commit mistaken identifications at a rate higher than young adults. Research has also indicated that people are better able to recognize faces of their own race or ethnic group than faces of another race or ethnic group.

Incident characteristics, such as the use of force or weapons. The presence of a weapon during an incident can draw visual attention away from other things, such as the perpetrator’s face, and thus affect an eyewitness’s ability to identify the holder of the weapon.

Links:
Live police lineups do they work?
http://www.ojp.usdoj.gov/nij/journals/258/lineupchart.html

Eyewitness Evidence Trainers Manual for Law Enforcement:
http://www.ojp.usdoj.gov/nij/pubs-sum/188678.htm

http://www.ojp.usdoj.gov/nij/journals/258/police-lineups.html