Can Lineup Administrators Blind to the Suspect's Identity Influence Witnesses' Decisions?

It is advocated that police lineup administrators should be blind to the identity of suspects to prevent them from influencing witnesses' decisions. Yet, it has been found that a lineup administrator who is blind to the suspect's identity may bias a witness's decision if he or she has previously administered the lineup to another witness to the same crime. In the present two experiments these findings are examined and expanded upon. Administrators blind to the suspect's identity presented a sequential lineup to a confederate and then a naïve witness under the manipulations of the confederate witness's decisiveness, confidence and decision speed. The findings of the previous study were not replicated; however, the second witness identifications matched the confederate's selection significantly more often when the confederate's decision was rapid rather than slow. Given the potentially dire consequences of such an effect, it is argued that different blind lineup administrators should be used for each witness to a crime.