Proper Eyewitness Identification Procedures
Green, Marc, Law & Order
Defense council may be able to undermine eyewitness identifications on several grounds. First, visibility conditions may be poor: low light, poor weather, etc. Second, many research studies report that even under good visibility, humans are poor at facial identification. However, the validity of this research, much of which is performed in artificial and unrealistic situations, has often been challenged.
Third, the procedures used to obtain the identification may be biased. To prevent loss of credibility, eyewitness identification tests should be performed under carefully controlled and scientific methodology.
Jurors treat eyewitness identification as compelling evidence in both civil and criminal trials. The strength of eyewitness testimony is demonstrated by a study (cited in Loftus and Doyle, 1992) that recorded verdicts in a mock trial. Two separate sets of the jurors heard evidence differing only by the presence or absence of an eyewitness. With no eyewitness, only 18% of jurors gave guilty verdicts.
Addition of eyewitness identification increased the proportion of guilty verdicts to 72%. Moreover, even when the identification was impeached, the guilty rate was still 68%. Several other studies have similarly found that juries tend to base their decision on confident eyewitness identification even when other factors (such as poor visibility or bias) question its validity.
Although jurors rely heavily on eyewitness identification, there is overwhelming evidence that eyewitness identification is highly fallible and that eyewitness confidence is a poor guide to accuracy. A recent study (Wells, et al., 1998) examined the first 40 cases where DNA exonerated wrongfully convicted people. In 90% of the cases, mistaken eyewitness identification played a major role. In one case, five separate witnesses identified the defendant. Huff (1987) studied 500 wrongful convictions and concluded that mistaken eyewitness identification occurred in 60%. This is an amazingly high number since eyewitness identification is an important factor in only five percent of all trials (Loh, 1981).
Cutler and Penrod (1995) examined eyewitness identification accuracy from controlled studies performed in a natural setting. In the typical study, a person enters a convenience store and performs some memorable action (such as paying in pennies) to ensure drawing the clerk's attention. Later the clerk views a photospread and identifies the customer.
The percentage of correct identification ranged from 34-48% and the percentage of false identification was 34-38%. It is hard to know how far to generalize such studies, but they suggest that eyewitnesses are almost as likely to be wrong as to be correct when identifying strangers. Moreover, these results occurred until highly favorable circumstances: extended duration, good lighting, clear visibility and no weapons focus.
Why is mistaken identity so common? One reason is poor encoding at time of initial perception. This could be due to poor visibility (bad lighting, brief duration, long distance, etc.) or to the tricks played by human perception.
A second reason is faulty memory. Memory has several quirks which affect reliability, including: low resolution, a remembered face is not as clear as one actually viewed; the tendency for memories to be constructed so that missing information is supplied from expectations/biases or from an external source (TV, newspaper, other witnesses, the police, etc) or from other memories; and systematic perceptual distortions in memory.
A third reason for error lies in the procedures used during photo-identifications and lineups.
From a scientific view, valid finding of fact requires that the outcome is not contaminated by confounding variables (those other than the ones whose effects are explicitly being measured) or biased toward desired results. Moreover, each observation should be independent and unrelated to any other. …