Yvonne Cook examines the methods being used to improve the accuracy of eyewitness evidence
The phrase "I saw it with my own eyes" can sound convincing in a court of law. But eyewitness identification has been responsible for serious miscarriages of justice. The US Innocence Project, which is dedicated to using DNA evidence to overturn wrongful convictions, estimates that mistaken eyewitness identification plays a role in more than 75 per cent of its cases.
Professor Graham Pike, a member of the Forensic Psychology Research Group based at the Open University, is one of a number of psychologists who have been working with police to reduce the number of misidentifications. He says the key to understanding why eyewitnesses can be so unreliable lies in the psychology of human memory.
" Memory is not like a video of an event which can be replayed endlessly and is always perfect. Human memories alter over time, and are very suggestible," he says. "In a classic experiment carried out by the psychologist Elizabeth Loftus, witnesses were asked to recall details of a road accident they had seen on film. She found that when the witnesses were asked 'how fast were the cars going when they smashed into each other?' they remembered the cars as travelling faster than when they were asked 'how fast were the cars going when they hit each other?' Simply changing one word in the question influenced the way people remembered the event."
In the UK, research such as this has transformed the way witness evidence is collected. The police are now aware that asking a witness "What colour hat was the man wearing?" is likely to cause the witness to remember the man as wearing a hat, even if he wasn't. Avoiding such leading questions is standard practice in police interviews today.
Under the Police and Criminal Evidence act, eyewitnesses taking part in an identification parade are routinely told that the person being sought for the crime may or may not be present in the parade line-up. Research has shown that this tactic reduces the number of misidentifications. By contrast, asking witnesses "who do you think it is?" suggests that the guilty person must be present in the line- up, and increases the subconscious pressure to pick someone, even if the guilty person is not there.
Psychologists have also demonstrated that people's memories are less reliable when they are under stress. One direct result of this is the rise of the video identity parade. The Forensic Psychology Research Group worked with West Yorkshire Police in the 1990s to pioneer VIPER, which is now used by more than 30 police forces. Instead of a viewing a line-up of people, the witness or victim is invited to pick the perpetrator from a series of video clips of faces. "This is much less stressful for the witness than coming face to face with the offender at a live identity parade," says Professor Pike. VIPER also builds on research which showed that presenting the faces of suspects one by one reduces misidentification. If witnesses are presented with a number of faces all at once, they will be more inclined to pick out "the best match", and they will tend to do so even if it is not the perpetrator.
The work of the Forensic Psychology Research Group was the inspiration for the BBC2 series Eyewitness, funded by the OU, in which crimes were staged in front of participants and …