In general, eyewitness testimony is not nearly as reliable as people think it is. People tend to have the idea that an eyewitness, so long as he or she is not biased, is the best possible type of evidence to show that a defendant has actually committed a crime. However, this is not true.
Eyewitnesses can very easily make important mistakes. This is why many people who have been exonerated by DNA evidence have been identified by eyewitnesses. Eyewitnesses can make mistakes because they overestimate how well they can identify individuals from a long distance away. They can make mistakes because of the fact that their memories change from the time that they see an event to the time that they are questioned about it. They can make mistakes if police interviewers plant ideas in their minds whether purposely or accidentally. They can make mistakes because of the emotional nature of the situation. A person who has seen a crime happen may well be shocked by what they have seen and their memory may be affected by that shock.
For these reasons and others, eyewitness testimony is not particularly reliable.
Iowa State University experimental social psychologist Gary Wells, PhD, a member of a 1999 U.S. Department of Justice panel that published the first-ever national guidelines on gathering eyewitness testimony, says Loftus's model suggests that crime investigators need to think about eyewitness evidence in the same way that they think about trace evidence.
"Like trace evidence, eyewitness evidence can be contaminated, lost, destroyed or otherwise made to produce results that can lead to an incorrect reconstruction of the crime," he says. Investigators who employ a scientific model to collect, analyze and interpret eyewitness evidence may avoid incidents like Olson's potentially flawed identification of the Fairbanks suspects, he notes.