An eyewitness to a crime with a faulty memory can seriously distort other witnesses' testimony if they discuss what they saw, research by Aberdeen University psychologists has revealed.
Witnesses influence others not by the force of their personality, but simply by being the first to mention something, it was found.
The Aberdeen team led by Amina Memon has just completed a 13-month study funded by the Economic and Social Research Council, which included two key projects.
In the first, witnesses watched a simulated crime and were then presented with a misleading account of the event, either in conversation with a "fellow witness", in fact a stooge, or in a written statement. Misleading information from the stooge had much more influence, with 44 per cent of witnesses "remembering" things they had not seen, compared with 31 per cent of those with the written report.
In a second study, co-witnesses were led to believe they had seen an identical event, but there had been key variations. If one witness mentioned something the other had not seen, almost two-thirds did not challenge it. And in 20 out of 37 instances of disputable events, co-witnesses "remembered" the wrong version.
Referring to the Oklahoma bombing case, researcher Fiona Gabbert said the FBI spent a long time searching for Timothy McVeigh's alleged accomplice, "seen" by three witnesses. It now seems that two had been unintentionally influenced by the third, who months later confessed he might have confused events.
The team has won two years' Leverhulme Trust funding to investigate further.