A fragile mind

For all the advances in forensic science, expert and surveillance evidence (for which see 'Behind bars' passim, and without doubt futurim) the majority of criminal trials depend on eye witness evidence. Eye witness evidence depends on memory, and memory is a fragile, corruptible and partisan tool. Just how fragile is being demonstrated at the moment by a BBC and Open University series of 'Eyewitness' programmes running on Sunday nights, developed in conjunction with forensic psychologists and Greater Manchester Police.

A group of people who thought they were volunteering for straightforward research into memory were taken off to a pub for lunch on the second day '“ and saw a murder take place before their eyes. Only one of their group knew that everything they saw was staged by actors: her role was to disseminate false information to the others. The pub was fitted up with cameras which recorded everything said and done.

The 'murder' itself was shocking to see '“ partly because it was so lifelike, and partly because not a single one of the group tried to intervene. Lack of intervention in those circumstances is itself a well known psychological response called the 'bystander effect' which operates on witnesses in groups.

Single witnesses intervene, even if only by calling for help, but it seems that groups of witnesses become inhibited in any humanitarian response by the presence of others.

As it was, they were all in pole position to see and remember what happened, and, as in real incidents, had been shocked and even frightened by the events. They were then interviewed, for about four hours each, by police officers who behaved throughout as though the exercise was a genuine incident '“ although by the time of the interviews the witnesses had been told it had been staged.

The police officers who conducted the interviews were trained in cognitive interview techniques, a psychologically-based method where the interviewee is allowed as long as they like to 'free recall' without being questioned at all and is then focused in on the incident itself: the analogy used is that memory is a series of rooms into which the witness is invited to enter, moving through until the incident itself is reached, gradually focusing in to the main facts. Probing and follow-up questions are then asked on the key points.

Manchester police seem to be the world leaders in this method, and, as is their apparent practice, all the interviewees were both voice recorded and videoed. The method takes unusual care to avoid leading questions, assumptions by the interviewer and contamination, but, even so, the results were startling. The two witnesses nearest the staged murder, and in a position to give the best evidence, were interviewed first. One of them warbled on for over two hours in the free recall exercise '“ which covered everything from the colour of the pub carpet to whether or not he liked salt on his peas '“ and failed to uncover anything of relevance at all. The other witness was convinced the 'victim' '“ who had been abusive and aggressive to his girlfriend at the start of the incident '“ was the murderer.