Identifying criminal suspects from eyewitness descriptions can be a hit-or-miss affair for police. No two witnesses give the same information.
New methods of merging and manipulating photofits are now boosting law enforcers' chances of finding the face to match the crime.
When a witness describes the face of a suspect villain to police they will pick out details which may be correct but when put together give a misleading and poor likeness. "If four people have attempted to produce a likeness they'll be wrong in four different ways," said psychologist Dr Peter Hancock, of Sterling University, at the British Association Festival of Science in Glasgow yesterday.
"They get all the features right but somehow the face is wrong."
By combining descriptions taken from a number of witnesses, the scientists have found that likenesses can be greatly improved. They achieve this by taking individual e-fit pictures - the electronic version of a photofit as used conventionally by police and morphing them on a computer into a combined face.
In a test, Dr Hancock used four e-fit images of a famous face - actor Robert Carlyle - each built up from descriptions by four people and combined them into one using the morphing technique. Given a multiple choice of six possible owners of the face the morphed face produced a 90 per cent successful identification compared with a next best of 60 per cent by looking at individual e-fits.
"Each one of the faces will capture some aspect of the real person. Combining them gives more aspects of the real person. Showing all four at once doesn't work so well," said Dr Hancock. So far Dr Hancock's study has concentrated on young, white adult males. "They are the group responsible for most crime in these isles," he said.
Crime investigators are already interested in Dr Hancock's work but to bring convictions using it would need a change in the law. Morphing descriptions from separate witnesses means that criminal evidence from different witnesses has to be combined. This is not allowed under the current law in England and Wales. "Morphed pictures aren't defensible by one witness under current law," said Dr Hancock.