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.

Filling the gaps

There was no psychological explanation given for why the first witness was so hopeless, but a police officer with a grounding in forensic psychology explained his understanding of the mistake made by the second witness. He had fallen into the trap which bedevils accurate and impartial memory '“ the human brain's main function is to make sense of information it is given, and will do so using the witness' own principles and beliefs.

The witness who got it so wrong did so because he was of an age and type who believed that anyone who was aggressive to women was a wrong 'un, and could not therefore be a victim. One of the psychologists explained that 'the mind makes up the world for you' '“ it fills in the gaps between bits of information, and joins the dots where there are none. Deliberately, no weapon was used or shown in the exercise, although the 'victim's' girlfriend was heard to cry out: 'He's been stabbed.'

The 'stooge' witness told everyone during the incident that she had seen a weapon. Probably as a result of this, another witness described in graphic detail, with gestures, how she had seen the murdered actively using a knife. The probing question was: 'Did you actually see a knife?' The answer was: 'No.' An unskilled interviewer, and criminal practitioners will know there are plenty of those around, would have asked questions about what the knife looked like, and undoubtedly the helpful witness, now confident that there actually was a knife as one had just been confirmed by that question, would have found some details to recall.

In another unrelated exercise, witnesses were asked to recall and describe a series of objects. A witness described a cushion '“ inaccurately '“ saying more than once: 'If there was a cushion.' Uncertain of what he had seen at all, he made up details to please the interviewer. The programme demonstrated that even using good interviewing techniques, based on an understanding of how the memory actually works, independent witnesses with no axe to grind can be fundamentally unreliable. Not always of course '“ overall the evidence gathered accorded with the facts of the exercise '“ but the programme not only graphically demonstrated the risks of eye witness evidence, but explained in part how memory functions.

Filling in the gaps, making sense of information according to our beliefs, false memory, a herd instinct that assumes other people are right, and, overwhelmingly,

shutting down when there is too much information to process '“ these are psychological impediments to accuracy. And these all clash with the criminal law tradition that memory is inviolate, that honesty and intelligence produce accurate remembering, and that the witness who remembers most is the witness who remembers best. Perhaps we should consider instituting 'Turnbull' type memory directions to the jury based on forensic psychology '“ a warning that memory can forget the truth.