In all the interviews examined, police officers excluded important pieces of information and possible clues. On average they missed out 14 items relevant to the investigation and in one case excluded 38.
A large proportion of the officers also ignored information that contradicted earlier evidence or the opinion of the interviewer.
Sixty-five per cent of the inquiries were either leading questions or considered 'risky' because they were likely to produce a misleading or distorted answer. The officers were also criticised for talking too much. In one example a man who saw a brawl in a pub was only allowed to speak for 79 seconds.
Reformers say the study, which was carried out in West Yorkshire, is a damning indictment of police interview standards. As well as leading to false and distorted statements the police are concerned that potentially vital lines of inquiry could be missed by sloppy and inaccurate note-taking.
The author of the report yesterday urged the Home Office to introduce compulsory tape recordings for all witness statements, as they do with suspects who have been cautioned.
The study was carried out by Inspector Maxwell McLean, of the West Yorkshire police force. He compared the official notes taken in 16 interviews of witnesses in 1992 with a tape recording of each event. Insp McLean, who presented his findings in London last night at a seminar called A New Look at Eye Witness Testimony, organised by the British Academy of Forensic Sciences, said that the results were typical of practice throughout the country.
He said: 'All 16 statements were signed as a true record by the respective witnesses yet not one contained all the relevant information being offered by that witness.' In two examples an officer questioning a witness to a robbery failed to note two possible clues about the description of a car and a potential witness. The statements he ignored were: 'I saw a sticker in the back of the window' and 'I explained what had happened to the person in the office'.
Insp McLean also noted: 'Witnesses will often feel pressured to live up to the officers' expectations that by being asked a question the answer should be known. They are particularly suggestible to questions asking for affirmation and to leading questions.
'When an answer has been given, however uncertainly and haltingly, it becomes a 'fact' and the witness leaves all doubt behind, especially if the interviewer seems pleased with the answer.'
Insp McLean compared witness statements with those of suspects who had been cautioned and concluded: 'It would appear that the witness is in much greater danger of being led than the suspect.'
On four occasions - during three interviews - the police wrote down a fact that was the opposite to what the witness was saying. 'So, not only can information of real relevance be left out of written statements, but, where necessary, for the sake of plausibility, contrary information may be included,' he said.
He added that the mistakes his study uncovered 'are being repeated every day by police officers throughout the country'.
'The only way to resolve this problem is to record conversations between police officers and witnesses,' he said.
Currently, only interviews of suspects who have been cautioned for an alleged crime must be tape recorded. A Home Office spokeswoman said that there were no plans to extend the scheme to witnesses because it was unnecessary and would be extremely expensive and time-consuming.Reuse content