Increasingly sophisticated computer progammes are helping the police to identify criminals.

John Dean looks at the lastest technology in the fight against crime.

IT is the technology which has given police a powerful new weapon in the fight against crime by making it easier to identify - and track down - criminals. Computer programmes are constantly being developed which take witnesses' descriptions and produce realistic, high- quality impressions of wrongdoers' appearances.

The technology, which is also making CCTV more effective, is moving at breathtaking speed, and leading the police service's response to the constant innovations is an experienced Durham police officer with 27 years in the job.

Detective Chief Superintendent Ian Scott, head of Durham CID and a veteran of many high-profile cases, has for the last three years been chairman of the Association of Chief Police Officers' (ACPO) working group on facial identification.

His task is to encourage police forces throughout the country to take advantage of the new technology.

The software is being produced by commercial companies, a number of them linked to universities or run by ex-police officers, and all the systems operate on the premise that, just like fingerprints, faces are unique.

Methods include:

E-fits: these replaced the old identikit image but work on the same principle. Witnesses choose from databanks of computerised images and, working with a skilled operator, select the right facial features, such as eyes and noses, to create an accurate picture of the suspect, which can then be released to officers and the media. What makes it different from the old identikit system is the massive number of facial features from which witnesses can choose.

Det Chief Supt Scott saysd: " When I started out we were using identikits and you were presented with a face shape on a piece of card containing slots. You then picked eyes and noses and the like which were on pieces of card which could slide into slots on the face.

"It was effective and the current technology works on the same principle, only using computer software which offers hundreds of options. However, the technology does not replace the human element. It is a tool because it still depends on the skill of the operator to interview the witness and extract the relevant information. And it still depends on the witnesses to recount accurately what they observed."

Morphing: this is still being developed and is not being used by police forces even though commercial software packages are on the market. Morphing makes it possible to take different witnesses' descriptions of the same person and blend them together electronically to create a single face. The problem is that it has been created by the computer and not by an individual witness, which can create a misleading impression.

Facial mapping: already in use. When suspects are arrested, exact measurements of features such as noses and ears can be compared with even poor CCTV pictures. Experts can then prove that the wrongdoer captured on film is the same as the one in custody, based on the premise that everyone's facial features are different.

Det Chief Supt Scott says: "This can work with even the most grainy CCTV images. We can take them to facial mapping experts, whose evidence has already been tested in a number of court cases, and they can testify in court that the person on the CCTV picture is the same one sitting in front of the jury."

Dr Leslie Bowie, research director of Nottingham-based ABM, which developed the Facial Verification Bureau used by many police forces to turn CCTV pictures into forensic evidence for court, says: "Police forces are recognising the power of CCTV as a crime-fighting tool and are increasing their investment in this technology - the UK now has the highest concentration of CCTV cameras in the world. There is seldom a crime case that does not include CCTV evidence."

Det Chief Supt Scott believes the police service must embrace the developing technology but that it must not replace traditional investigative techniques.

He says: "I always stress that an e-fit is only a tool and it has limited evidential weight. It is only a clue: we are not going to take an e-fit into court and say 'that is what our e-fit looks like and that is what the defendant looks like, so convict him on that basis'. An e-fit simply helps get us to the point of arrest. It does not replace traditional methods of investigation. It is part of the toolbox available to police officers.

"However, anything which aids the identification of suspects needs to be welcomed with open arms and we need to ensure that officers are using, and have adequate knowledge of, the current technology. Officers need to use it properly and be aware of its potential. The technology is continuously moving forward in providing ways of helping investigations."

Det Chief Supt Scott has just been placed in charge of a national project established by the Home Office to develop the most comprehensive library of pictures yet of prisoners for a national database. To be up and running by December 2005, the project would give police officers access to more information than they have ever had before.

Det Chief Supt Scott says: "At the moment, we take the traditional straight-on photograph of the prisoner but that does not tell us information such as what the suspect looks like from one side or the other, or what his gait is like. Under the new system, moving pictures would be taken from different sides and the suspect - regardless of whether or not they are eventually charged - would be filmed walking.

'That information would then be placed on the Police National Computer and could be accessed by any police officer. To take an example, a man is arrested in one town under the name John Smith but is then arrested in another town having given a false name, Fred Jones. This system would allow the officers to examine the database and prove that John Smith and Fred Jones are one and the same person. It would also tell if he was suspected of other crimes, if there are cases outstanding, or court appearances pending. That is very useful when it comes to travelling criminals.

"There is also technology in use now which takes fingerprints and palm prints digitally. All the suspect does is run the hand over the screen, and that information can be accessed electronically by fingerprint bureaux staff to confirm someone's identity and search outstanding fingerprints left at crime scenes.

"I know there are civil liberties issues but this is what the Government wants to see and, looking into the future, I think it will happen. We are making better use of the information and technology available to us - the result is that there are fewer places for the criminals to hide."