Parietal lobe

Scientists today revealed a new psychological tool that helps witnesses “freeze” the memory of crime scenes in their minds.

The technique, developed by the University of Portsmouth, involves witnesses being given a general questionnaire soon after the incident in a bid to prevent natural memory decay.

Dr Lorraine Hope developed the self-administered interview (SAI) project, funded by the British Academy, with the help of police forces in England and Scotland with the aim of improving witness statements.

The SAI asks a witness to write down as many details as possible about the incident rather than give a brief initial outline of events as currently required by police in many situations.

Dr Hope’s research has shown that witnesses can recall forensically important information 42% more accurately using the SAI than those asked to ‘report as much as they can remember’.

And this increases to 44% for information about people involved in the incident.

Also, when witnesses were asked to recall events seven days afterwards, those who had completed the SAI reported details 30% more accurately than other witnesses.

Dr Hope said the completeness and accuracy of witness evidence decreases as the delay between witnessing an incident and recalling it increases.

She explained: “Decades of research in cognitive psychology demonstrate that memory decay, or forgetting, occurs rapidly at first.

“In a witnessing situation, this ‘forgetting’ will occur naturally and within hours of the incident.

“As the delay between witnessing and formal interview increases to days, memory decay will level off. However, by that time, many useful and forensically relevant details or clues may be lost forever.”

She added that current techniques of asking witnesses for a brief outline rather than for as many details as possible could actually damage witnesses’ memories.

She said: “The forensic implications of these findings for current police practice are considerable.

“At present, witnesses are likely to engage in a very brief initial interview prior to giving a full statement at some later date.

“This very brief initial interview may actually have a detrimental effect on the ability of a witness to fully recall the incident at a later occasion.

“In other words, only the memory for the brief outline is strengthened, not the memory for the details, which can sometimes become harder to recall as a result.

“An early recall attempt serves to protect or ‘freeze’ the memory against the course of natural forgetting.”