Forensic psychology
Forensic psychology

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Forensic psychology

2.1.2 Co-witnessing

Figure 3

It is important to consider whether there was more than one witness to a crime, and how each witness’ memory and testimony might be affected by talking to other witnesses.

Helen Paterson is a Senior Lecturer in Forensic Psychology at the University of Sydney, Australia, and a world expert on co-witnessing, a term that refers to crimes that are witnessed by two or more people who then share accounts of what happened. In this co-witnessing interview, Helen describes the impact that co-witnessing can have and how this topic has been researched.

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What sparked your interest in the effects of witnesses discussing events?
Witnesses tend to discuss the event with one another. This happens very reliably and consistently. And just to give you an example there is one story I heard about a man who was actually writing his thesis, this was many years ago, and I like this story because I was writing my thesis at the time I found out about him. What happened was he was actually wanting to write the final version of this thesis, and this was back in the day when people used typewriters. So he went up to the shops to purchase some new ink for the typewriter. He came back home and started to work on his thesis. A little while later there is a knock on the door and it's the police. And the police have come to arrest him and charge him with bank robbery. Apparently while he was at the shops he had robbed the bank. Well, it turns out that he was actually found innocent and one reason that he suggests that he was wrongfully charged with this crime was because one person had mistakenly identified him and then spoken to others and other people began to believe that he was the one who committed this crime. What's quite interesting to know for many of the people perhaps listening is that this man is actually very well known in the UK. His name is Peter Hain and he is a current member of parliament in the government and he was actually leader of the House of Commons under Tony Blair.
How did you go about investigating the impact of witnesses discussing what they had seen?
What we decided to do was we wanted to survey witnesses to find out how common this was and what we found in an initial survey that we gave out, the vast majority of witnesses report that there are actually other witnesses present when they view the event.
When we then went on to interview the people who had been around multiple witnesses when they - when they saw the event we found that the vast majority, that is 86 per cent, reported they talked to other witnesses about the event. We asked them what they talked about and the number one reason they talked about the event with one another was they're providing information. So they're actually talking about details of the event with one another.
I conducted a study and we wanted to compare to see how much information people - post event information people would incorporate into their memory accounts of an event if they encountered this information in one of several different ways. And whether they encountered the information through leading questions, which is commonly studied through reading about it in the media report or through co-witness information. And there were two different types of co-witness information we compared. Sometimes when witnesses discuss the event with one another we call this direct cowitness information. Or sometimes witnesses can encounter information indirectly, that is through a third party. For example if a police officer says oh the other witness mentioned that - that the suspect - that the culprit had blue eyes. Do you agree with this statement? So what we did was we had participants view an event and then we gave them post event information through one of these different methods either indirect, co-witness information, direct co-witness information, media report, leading questions or we had a control condition that didn't give any post event information. With this post even information we gave them some accurate information and we also gave them some items of inaccurate information.
What did your findings reveal?
What we found overall was that participants who encountered this information drew on either direct co-witness discussion or indirect and co-witness information. They were far more likely to include this information in their reports than those who encountered the information through leading questions and media reports. So this is actually suggesting to us that co-witness information is extremely influential and whether it be accurate information or inaccurate information they're far more likely to incorporate this information into their account of what happened during the events.
What we find is that co-witnesses reliably and consistently report information that they receive from a co-witness after an event. This is an extremely strong effect and it's been replicated in many studies. Essentially if you take Asch's conformity paradigm and the misinformation effect paradigm bring them together, you get a very strong effect. In fact I've never conducted a study where I haven't found the co-witnesses are very influential for memories.
Given your findings, is there anything that can be done to reduce co-witness effects?
In fact the effect is so powerful that you know we just can't get rid of the darned effect and that's been our problem more than anything else. We've tried a variety of different methods to try to see if we can get witnesses to discount the information that they've been given from a co-witness and only report their own memories for the event. And we find this actually doesn't work. We can't eliminate it. We can't stop them from reporting the co-witness information because it seems to become part of their own memory for the actual event.
In general, legal authorities would prefer it if witnesses don't talk about the event with one another. For example the legal concept of hearsay embodies the notion that a witness's assertions should be based on their own experiences and not those of another and actually there are guidelines that exist in the United Kingdom which suggest that witnesses should be separated and instructed not to discuss the event with one another.
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Remember that our crime was witnessed by two people, so when evaluating the evidence they provide you should take the effects of co-witnessing into account.


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