Skip to 0 minutes and 0 secondsGRAHAM PIKE: You're about to see video footage of a staged crime. Please watch it carefully.

Skip to 0 minutes and 50 secondsDo you think you would make a good witness if you were now interviewed by the police? Would you be able to remember everything about the crime? Can you remember what the person was wearing? Can you remember what the person took? Can you remember how many computers were in the office? Did the person have to unlock the door before entering the office? Although details such as these are important, perhaps the most important information the witness can provide relates to the identity of the perpetrator. As well as describing the appearance of the perpetrator, witnesses are also often asked to asked to identify the perpetrator from an identification parade.

Skip to 1 minute and 21 secondsOf course, the police first have to find and arrest a suspect before they ask the witness to make an identification, which usually means a gap of 4 to 6 weeks between the crime and the identity parade. So let's see how good a witness you would be. In a moment we're going to show you a photo line-up. There will be a letter next to each of the photos in the line-up. All you have to do is work out who the perpetrator is and remember their letter.

Skip to 2 minutes and 3 secondsLike most witnesses, you probably didn't find it that easy to work out what the perpetrator looked like. So let's work out how you did. Did you pick one of the letters? I'm afraid that if you picked anyone from the identity parade, you made a misidentification. The perpetrator of the crime you saw previously wasn't in the parade, so if you picked out anyone you picked out an innocent suspect. So if you did identify an innocent suspect - why was that? Psychological research has pointed to a number of reasons that could explain this. Amongst these are the fact that our memory for unfamiliar faces is very inaccurate.

Skip to 2 minutes and 40 secondsThe person you saw commit the crime was unfamiliar to you - you only saw them for a few seconds. It's therefore very hard for you later to identify them, to recognise them. Secondly, you saw all the faces in the identity parade at the same time - that is, they were presented simultaneously. When you see faces in the identity parade at the same time, what you tend to do is try to pick the best match for the perpetrator, even if that person isn't the perpetrator. So you look amongst all the faces and you pick the one that most resembles the perpetrator, even if it's not them.

Skip to 3 minutes and 13 secondsThirdly, it's possible that you picked someone out from the line-up because I told you to. At the beginning of the identity parade, the instruction that was used was a leading question. It suggested to you that the perpetrator was going to be in the parade, because I said "Pick out who it is and remember their number". So maybe the reason you picked someone out was because you were told to. Psychologists in the police have worked hard in the UK to overcome these problems, so suggestive questions are not used and the faces are shown one at a time to avoid witnesses simply picking the best match.

Skip to 3 minutes and 47 secondsHowever, it is very hard to overcome the fact that our memories tend to be very inaccurate. Misidentifications can lead to someone being prosecuted for a crime they did not commit. In 2007 DNA evidence finally exonerated Jerry Miller, who had spent 24 years in prison for a rape he did not commit. His conviction was based on evidence from 2 eyewitnesses. Their misidentification led to an innocent person being imprisoned for most of their adult life, whilst the real perpetrator walked free. Jerry Miller's case was the 200th case the US Innocence Project successfully appealed using DNA evidence. Eyewitness identifications played a role in 77% of these wrongful convictions.

Mistaken identification

Eyewitness identification evidence is a critical component of many criminal investigations, but how accurate is it?

Psychological research has shown that making even small changes to the way police obtain eyewitness evidence can have a profound effect on its accuracy. Watch the video above and follow the instructions.

Reflect on how you did in the task and think about the implications for how your memory works. Do you think a witness’s memory of the perpetrator’s face should be trusted as evidence?

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This video is from the free online course:

Forensic Psychology: Witness Investigation

The Open University