Lineup Filler Selection

The Function of Lineup Fillers

Lineup fillers, also known as foils (an innocent person in a police lineup), serve the major purpose of testing an eyewitness's recognition memory for a criminal perpetrator so as to establish evidence that the suspect is guilty of the crime. Fillers also serve to screen out unreliable witnesses: Witnesses who identify foils may have a weak memory for the perpetrator or may be guessing. With respect to the problem of guessing, the probability that a witness will select the suspect from a lineup based on chance alone equals 1/k, where k equals the number of foils in the lineup. Having more options during the identification test decreases the probability that witnesses will identify the suspect by guessing alone. Additionally, presenting foils that resemble the suspect works toward preventing the witness from being able to deduce who the suspect is simply by eliminating improbable choices from the lineup.

Filler Selection Strategies

There are two primary filler selection strategies that have been investigated by researchers. First, foils may be selected for the lineup on the basis of their similarity to the physical appearance of the suspect, a procedure that is known as the suspect-matched strategy. Second, foils may be selected based on their resemblance to a physical description of the perpetrator given by the eyewitness, a procedure that is termed the perpetratordescription-matched strategy.

Two main concerns arise when foils are selected for the lineup on the basis of the suspect-matched strategy. First, if the suspect is not the culprit and is in fact innocent, then selecting the foils based on their match to the innocent suspect may result in a lineup in which the similarity of the foils to the perpetrator is low. This is a concern in cases in which the suspect is apprehended because he or she is physically similar to the description of the culprit given by an eyewitness. In such cases, the suspect may be the only one in the lineup that resembles the perpetrator. As a result, the innocent suspect might be frequently identified from lineups in which the foils are chosen on the basis of their match to the innocent suspect's appearance, a consequence that is known as the backfire effect. Another concern that arises when the foils are chosen for the lineup using the suspect-matched strategy is that if the suspect is in fact the culprit, then the foils could potentially be too similar to the suspect, and thereby decrease the odds that a witness who remembers the perpetrator can distinguish the guilty suspect from the foils.

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