Let’s say you’re a victim of a crime or you see a crime being committed. You concentrate your full attention on the perpetrator, because you want to remember everything, the color of their hair and eyes, face structure, skin tone, height, weight, what they are wearing and scars. You are certain that you remember this person in great detail. After the assault or after the crime is committed, you file a police report. Hours or days later, you are asked to identify the assailant in a police line-up. This is when mistakes are often made. Although you are certain that you remember the perpetrator in great detail, there are a lot of hidden influences that can hinder the accuracy of your memory about this person. For instance, if you were the victim of the crime, the stress and fear of the crime itself, could alter your memory of the assailant. Time lapse can cause your memory of the events or person to be shaded. There are many new studies about the psychology behind police line-ups and how a person can be easily influenced by the police officer to pick the “right” person. Although witnesses are told that the perpetrator might not be in the police line-up, the witness is inclined to believe that someone in the line-up is responsible for the crime, especially if the suspects are physically similar to each other. This identification testimony can be very convincing to a jury. Bad identifications in the context of police line ups and in other contexts have resulted in false imprisonments. Advancements in DNA testing have helped decrease the chances of being wrongfully convicted. DNA while not without its own limitations has exculpated more than a few falsely accused persons.
Sources: 60 Minutes: “Picking Cotton”, National Science Foundation: Mistaken Idenity: How Feedback “After the Fact” Influences Eyewitneses http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=100715&org=SBE