One particular aspect of police investigations that psychological research has managed to help the police with is eyewitness identification. Most of us are familiar with the concept of an identity parade. That’s where the suspect - and at that point in the investigation it’s the suspect, not the perpetrator, the police don’t know whether this is the right person or not - the suspect and eight or nine people that look like them are placed in the room and the witness walks up and down and picks the person they think committed the crime.
Now there’s a great deal of research of human face recognition, so these are the processes that go in our mind that allow us to recognise faces, and this research has a lot to say about eyewitness identification as well. In a similar way to interviewing an eyewitness, this research has found that it’s very important to ask the witness the right questions when they’re seeing a parade. For a start, if I was to say to a witness, “Who do you think it is?” I’m suggesting to the witness that the perpetrator’s actually present, so even if they’re a bit uncertain, because I’ve said, “Who do you think it is?” they will pick someone. So instead of saying, “Who do you think it is?”, the Police and Criminal Evidence Act in the UK mandates that a particular formation of question is used. So the witness is told, “The person you saw commit the crime may or may not be present. If you think that they are present you then go ahead and choose who you think it is.”
Now that’s simple and it is a very simple element to the question, radically reduces the number of misidentifications made. Simply by saying to the person the perpetrator may or may not be present, what you’re saying to the witness is you don’t have to pick someone, the right person might not be there. And that simple instruction reduces misidentifications.
The other thing that psychological research has found is that stress can have a very adverse effect on all of our cognitive processes, particularly and including how well we recognise a face. And you have to remember, the face you’re trying to recognise in an identity parade is an unfamiliar one. You might have only seen it for a few seconds so it’s a very hard task to do. If you’re stressed at the identify parade then your cognitive processes won’t form so well so reducing the anxiety and stress of the witness at the parade is very important. That’s one of the reasons in this country we no longer or very rarely use live identification parades. So instead of seeing a row of people who are actually standing in front of you, instead of actually coming face to face with the perpetrator of a crime, which you can imagine if you were the victim is a very stressful thing to do, instead you’ll see a video parade. So you won’t ever be in the building with the potential perpetrator, with the suspect. Their image can be captured in a different part of the country and certainly at a different time, put into a video parade and the witness can then come along later to the police station, again it could be in a different part of the country, and view the identity parade, so that reduces the stress and anxiety.
The other important thing about how video identity parades are done in this country are the faces are seen one at a time. Psychological research has found that if you show all of the faces in the identity parade simultaneously - so in America very often a series of photos are laid down in front of the witness and they’re asked to pick out the person - seeing them all at the same time what you tend to do is pick out the best match, even if it’s not a particularly good match you pick out the best match. If you see them one at a time it makes it very hard to compare one face to another, so you’re making a decision about each face on its own merits, so instead of picking out the best match you’re working out is that face the one I saw. Again, presenting the faces one at a time can significantly reduce the number of misidentifications.
So these simple things, the way that the identity parade is constructed and the way it’s conducted that psychological research has found out about, radically reduced the number of misidentifications, so they were improving the police investigative process.