There were several sightings of the chief suspect in west London near the time of April's shooting, and police have put together an E-fit of the man they want to question. But as the investigation enters its third week, the trail has gone cold.

Police have now turned to the low-profile, but cutting-edge National Crime Faculty, in Bramshill, Hampshire, for help.

Despite an E-fit of the suspect there are no new leads

A criminal psychologist is working with the team to build up a psychological profile of the main suspect.

The technique can give a remarkably accurate picture of a personality, including likely habits and preoccupations.

Psychological profiling was pioneered by the NCF, an internationally renowned think-tank for the latest in investigative techniques. It is now so popular that the NCF keeps a database of registered criminal psychologists.

Police investigating the Dando murder could also call on the NCF for a detailed physical description of the killer.

The National Crime Faculty could provide new ideas

Specialists at the Forensic Science Service, run from the NCF, can use DNA from forensic samples, like those taken from Ms Dando's doorstep, to draw up a description of the culprit.

Within a decade, scientists believe that they will be able to provide a full genetic "photofit" of a suspect's weight, height, facial characteristics, hair and eye colour from a single cell or a drop of blood.

The movements of the murderer after Jill Dando's death could also provide essential clues.

The NCF is developing a new technique known as geographical profiling.

It is based on a theory that criminals follow patterns they may not be aware of themselves. A criminal's movements - like the suspect's dash from Jill Dando's house, and his later bus journey from Fulham Palace Road to Putney Bridge - may tell police more than he thinks.

But the NCF's most important role could be to tell police if the suspect has murdered before.

Police searching for the Yorkshire Ripper were swamped by information

In a massive national database, it has exhaustive details of investigations carried out all over the country. They include murders, rapes, and abductions, both solved and unsolved.

Police can feed in the details of the case they are working on, and the computer will match it with any similar cases. Since the system began four years ago, dozens of murder cases have been re-opened.

The method was developed following the fiasco of the investigation into the Yorkshire Ripper murders.

The crimes took place across several police force boundaries, and different forces simply missed the links between the murders.